What You Will Learn
- The four main types of paid digital advertising and how each one works
- How ad auctions work — and why the highest bid does not always win
- What CPM, CPC, and CPA mean and when each applies
- How targeting works across different platforms
- How to measure whether your paid advertising is actually working
The Four Types of Paid Digital Ads
Paid digital advertising comes in four broad types, each serving a different part of the marketing funnel and reaching people in different ways:
Paid Search — Ads that appear in search engine results when someone searches a relevant term. The person is actively looking for something; your ad appears at the moment of intent. Covered in depth in the Google Ads guide.
Social Media Advertising — Ads shown within social media platforms (Facebook, Instagram, TikTok, LinkedIn, X). These interrupt people who are scrolling their feeds — they were not searching for your product, so you need to catch their attention and create interest from scratch.
Display Advertising — Banner ads and other visual ads shown across websites and apps. You have seen these on news sites, blogs, and apps — they appear in designated ad slots. Display is used for building awareness and for retargeting people who have visited your website.
Video Advertising — Video ads served before, during, or after video content on YouTube and other platforms, or as in-feed video in social media. Video can tell a story in a way that a text ad or banner cannot — but requires more production investment.
How Ad Auctions Work
Almost all digital advertising is bought through real-time auctions. Every time a person loads a page or app with an ad slot, an auction happens in milliseconds — advertisers compete to show their ad to that person, and the winner's ad is served.
The auction is not purely about who bids the most. Platforms weight both the bid amount and the expected relevance or quality of the ad:
| Platform | Auction Formula (simplified) |
|---|---|
| Google Search Ads | Ad Rank = Bid × Quality Score (relevance of ad and landing page) |
| Meta (Facebook/Instagram) | Total Value = Bid × Estimated Action Rate × Ad Quality |
| Display (programmatic) | Highest bid above floor price wins (first-price or second-price auction depending on exchange) |
This matters practically: an advertiser with a lower bid but a highly relevant, high-quality ad can beat an advertiser with a higher bid and a generic, poorly-targeted ad. It also means you should always focus on ad quality and relevance — not just on bidding higher.
What You Actually Pay For
Digital advertising has several different pricing models, each suited to different campaign goals:
| Model | What You Pay For | Best For | Risk |
|---|---|---|---|
| CPC (Cost Per Click) | Each time someone clicks your ad | Traffic, search ads, performance campaigns | Clicks that do not convert still cost money |
| CPM (Cost Per Mille) | Every 1,000 times your ad is shown | Brand awareness, display, video | Impressions that are never seen still cost money |
| CPA (Cost Per Acquisition) | Only when a conversion occurs | Performance campaigns with enough conversion data | Platform needs conversion data to optimise effectively |
| CPV (Cost Per View) | When someone watches a defined amount of your video | Video awareness campaigns | Views do not guarantee attention or recall |
Most beginners start with CPC (you only pay when someone clicks, which at least means they showed enough interest to click). CPM is used when your goal is simply visibility. CPA bidding is the most efficient but requires the platform to have conversion data to work well.
Display Advertising
Display ads are the banner ads and image ads you see on websites and apps across the internet. They appear in designated ad spaces on news sites, blogs, apps, and other content. Display is delivered programmatically — automatically matched to audiences through ad exchanges like Google Display Network and third-party programmatic platforms.
Display advertising has two primary use cases for small businesses:
Retargeting — Showing ads specifically to people who have already visited your website. This is the most effective use of display for most businesses. Someone who visited your product page and did not buy is far more likely to convert on a targeted display ad than a complete stranger. Google Ads and Meta both offer retargeting capabilities.
Awareness — Reaching new audiences at low cost per impression. Display CPMs are cheap (£1–5 per thousand impressions). But cheap impressions that no one notices or that appear in irrelevant contexts are not efficient. Display awareness works best for brands with strong visual assets and clear targeting.
For most beginners, display is worth exploring as a retargeting tool once you have traffic on your website — not as a primary acquisition channel from the start.
Video Advertising
Video ads are served on YouTube (via Google Ads), in social media feeds (Meta, TikTok), and through programmatic connected TV (streaming services). Video can communicate things that text and image ads cannot — emotions, demonstrations, brand personality — making it particularly effective for brand-building campaigns.
The main YouTube formats a beginner should know:
Skippable in-stream ads — Play before or during a YouTube video; viewer can skip after 5 seconds. You only pay if the viewer watches 30+ seconds (or the full ad if it is shorter than 30 seconds). The first 5 seconds must make the viewer want to keep watching. Best for brand awareness and consideration.
Non-skippable in-stream ads (15 seconds) — Cannot be skipped; you pay per thousand impressions. Higher attention guarantee than skippable. More expensive per view. Best for short, clear brand messages.
The production barrier is the main challenge for small businesses — video ads require scripting, filming, and editing. A well-produced 15-second ad that is authentically on-brand outperforms a poorly produced 30-second ad. Smartphone footage shot in good light with clear audio can be effective; professional production is not always necessary for early-stage campaigns.
How Targeting Works
Targeting is how you define who sees your ads. The available targeting options depend on the platform, but the main types across platforms are:
Demographic targeting — Age, gender, parental status, household income. Available on most platforms. Useful for products with clear demographic profiles.
Geographic targeting — Country, region, city, postcode, or radius from a location. Essential for local businesses; important for any business with a defined service area.
Interest targeting — Reaching people based on their interests, hobbies, and content they engage with. Meta and Google have extensive interest taxonomy options.
Behaviour targeting — Reaching people based on actions they have taken — recent purchases, travel behaviour, life events. Meta's purchase behaviour targeting (reaching people who recently bought in a category) is particularly useful for e-commerce.
Custom audiences (first-party): Uploading your own customer list (email addresses) and showing ads to those specific people. Or retargeting website visitors using a tracking pixel. These are the highest-performing targeting options because they are based on real data about people who already know you.
Lookalike / similar audiences: Platforms can find new people who share characteristics with your existing customers. Meta's Lookalike Audiences and Google's Similar Audiences use machine learning to expand your reach to statistically similar new prospects.
Measuring Whether Paid Ads Are Working
The fundamental question is: are you getting more value from customers acquired through paid ads than you are spending on those ads? This is measured through ROAS (Return on Ad Spend) for e-commerce, or CPA (Cost Per Acquisition) for lead generation.
For e-commerce: ROAS = Revenue from ads ÷ Ad spend. If you spent £500 on Google Ads and generated £2,000 in tracked sales, your ROAS is 4× (or 400%). Whether 4× is good depends on your gross margin. At 40% gross margin, a 4× ROAS means £800 gross profit on £500 spend — profitable. At 20% gross margin, a 4× ROAS means £400 gross profit on £500 spend — unprofitable.
For lead generation: What is the average value of a converted lead? If a new customer is worth £500 to you and your cost per lead is £25 with a 20% close rate, your cost per customer is £125 — and the economics are healthy. Set your target CPA based on what a customer is worth, not on an arbitrary round number.
Meta and Google report their own attribution — and they both tend to overclaim. A customer who clicked a Meta ad, then later searched on Google and clicked a Google Shopping ad, and then converted, will be counted as a conversion by both Meta and Google. The true number of conversions from any single channel is usually lower than the platform reports. Use Google Analytics 4 as an independent reference point.
Paid vs Organic: When to Use Each
Paid and organic channels serve complementary roles — they are not alternatives to each other.
| Situation | Use Paid | Use Organic (SEO/Content) |
|---|---|---|
| Need results now | ✓ Paid delivers immediately | ✗ Takes months |
| Testing new messages | ✓ Quick feedback on what resonates | ✗ Too slow to test |
| Building long-term traffic | ✗ Stops when budget stops | ✓ Compounds over time |
| Limited budget | ✗ Budget runs out quickly | ✓ Lower ongoing cost once built |
| Targeting very specific audiences | ✓ Precise targeting available | ✗ Reach is organic and less controlled |
| Building brand trust | ✗ Ads less trusted than organic content | ✓ Editorial content builds genuine authority |
The best digital marketing strategies use paid channels for immediate acquisition and organic channels for long-term compounding. Paid funds growth while organic is being built; organic reduces dependence on paid over time. Building both in parallel is the most resilient approach.
What to Read Next
You have finished this guide. Here are the best places to go deeper — all written for beginners, all from the Digital Codex reference library.
Sources & Further Reading
Every fact, statistic, and framework in this guide draws from official documentation, peer-reviewed research, or verified practitioner sources.
Meta's official documentation on how its advertising auction determines which ads are shown.
Google's official documentation on the Ad Rank formula and auction mechanics.
LinkedIn's official documentation on B2B audience targeting options.
TikTok's official advertising help documentation for beginners.
Social Media Advertising: Meta, TikTok, LinkedIn
Meta (Facebook and Instagram) Ads are the dominant social advertising platform for most consumer businesses. Meta's strength is its vast first-party data — it knows its users' ages, interests, life events, and behaviours in extraordinary detail, enabling precise audience targeting. Meta ads appear in News Feed, Instagram Feed, Stories, and Reels. Best for: e-commerce, local services, consumer products, app installs, events.
TikTok Ads are most effective for reaching younger demographics (18–34) and for brands whose products have visual or entertainment appeal. TikTok's ad formats are built around short video content that fits naturally into the platform's feed. Best for: fashion, beauty, food and drink, entertainment, and brands willing to invest in native-style video creative.
LinkedIn Ads are the dominant B2B social advertising platform. LinkedIn's targeting is based on professional data — job title, seniority, company size, industry — making it the most precise way to reach business buyers. The trade-off: LinkedIn CPCs are significantly higher than other platforms (often £5–15 per click vs £0.50–2.00 on Meta). Best for: B2B software, professional services, recruitment, corporate events.
Choosing the right platform comes down to one question: where does my target audience spend time? A solicitor targeting businesses should be on LinkedIn. A wedding photographer should be on Instagram and Pinterest. A gaming brand should be on TikTok and YouTube. Follow the audience, not the platform hype.