Google Tag Manager is a free tag management system that allows you to manage and deploy marketing tags (snippets of code or tracking pixels) on your website (or mobile app) without having to modify the code.

When Tag Manager is installed, your website or app will be able to communicate with the Tag Manager servers. You can then use Tag Manager's web-based user interface to set up tags, establish triggers that cause your tag to fire when certain events occur, and create variables that can be used to simplify and automate your tag configurations.

A collection of tags, triggers, variables, and related configurations installed on a given website or mobile app is called a container. A Tag Manager container can replace all other manually-coded tags on a site or app, including tags from Google Ads, Google Analytics, Floodlight, and 3rd party tags.