GTM Overview • Preview • Data Layer • Building Custom Variables
Google Tag Manager (GTM) is a tag management system that helps you deploy and manage tracking codes
(GA4, Ads, Meta Pixel, etc.) without constantly editing your website code. It’s the foundation for scalable, professional tracking.
Tags are the tracking scripts you want to run—like sending a GA4 event such as view_item or purchase.
Triggers tell GTM when to run a tag. Examples include:
page views, clicks, form submissions, scroll depth, and custom events.
Variables store values used by tags and triggers—like Click URL, Page Path, or dataLayer values such as product_name.
Variables are how you pass useful details into GA4 as parameters.
Preview mode is your safe testing environment. It lets you confirm that:
(1) the trigger conditions are correct, (2) the tag fires, and (3) variables contain the right values.
The data layer is a structured JavaScript object that stores information about what happens on the site.
For example, when a user clicks “View Course” or “Add to Cart,” you can push an event and details into the data layer.
GTM can then read that data and send it to GA4.
In this lesson, you saw how to create custom variables based on dataLayer values.
This is a critical skill because it allows you to pass meaningful event parameters like product name, course title, or category.
We’ll go deeper in upcoming lessons when we build real eCommerce tracking.
GTM becomes easy when you think in systems: define what to send (Tag), define when to send it (Trigger),
and define which details to include (Variables + Data Layer).