How to set up Google Tag Manager (and GA4 through it)

What Tag Manager is for

Google Tag Manager (GTM) is a container for tracking code. You install one snippet once, then add, change and remove tags (GA4, Google Ads conversions, Meta, LinkedIn, call tracking scripts) from the GTM interface without editing the site each time. Every change is versioned, so a bad change can be rolled back in a minute. For a site with one GA4 tag and nothing else, GTM is optional. Once a second or third tag arrives, or a marketer needs to change tracking without a developer, it pays for itself.

Step by step

1. Sign in at tagmanager.google.com, open the Accounts tab and choose Create Account. Use your organisation as the account, and set the country.
2. Create one container per website. Google suggests naming it after the site's top-level URL. Choose Web as the container type, then Create, and accept the terms.
3. Install the container. GTM shows two snippets: the script goes as high in the <head> of every page as possible, and the <noscript> iframe goes immediately after the opening <body> tag. On WordPress, Shopify and most site builders there is a setting or a plugin for this; do not paste the code into a single page template that some pages skip.
4. Add GA4. In the Workspace, create a new tag of type Google tag, enter your GA4 measurement ID (it starts with G-), and set the trigger to Initialization - All Pages (or All Pages). If the site already has a hard-coded GA4 tag, remove it, or you will count every page view twice.
5. Click Preview. Tag Assistant opens in a new tab; enter your site's URL and Connect. Your site opens showing Connected, and the Tag Assistant tab lists every tag that fired on each page and event. If the debug parameter breaks your site, untick Include debug signal in the URL.
6. With Preview still running, open GA4's DebugView (Admin, then DebugView) and confirm page_view and session_start arrive.
7. Click Submit, give the version a name that says what changed ("GA4 base tag, removed hard-coded gtag"), and Publish. Until you publish, only Preview sees your changes.

How to keep a container tidy

• Name things by pattern: "GA4 - Event - generate_lead", "Trigger - Form - Quote form". Six months from now someone else will read it.
• One person publishes. Workspaces let several people prepare changes, but conflicting publishes are the usual cause of tags vanishing.
• Use the data layer for business data. Ask developers to push values such as form name, plan or order value into window.dataLayer, then read them with Data Layer Variables, rather than scraping the page with CSS selectors that break on the next redesign.
• Consent first. In regions that need consent, tags must respect the visitor's choice. GTM's consent settings and Consent Mode are covered in GA4 Consent Mode v2.
• Agencies: work in the client's own account, as a user. If the container sits in the agency's account, the client loses its tracking history when the relationship ends.

What to set up next

With the base tag live, add the events that matter: form submissions (how to track form submissions in GTM), phone-number clicks, and purchases (GA4 ecommerce tracking). Then exclude your own team's traffic before anyone reads a report.