Google Tag Manager is Google’s free tag management system (TMS) where you can quickly and easily update measurement codes and related code fragments (tags) on your website or mobile app.
When Tag Manager is installed, the 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.
It’s a really useful tool to implement code, analytics snippets, even changes to your website if you don’t have CMS access.
Tag Manager is one of the easiest ways to set up all the tracking codes for your analytics in one go, for example:
Google Analytics
Google Search Console
Google Ads tracking
Facebook pixel tracking.
It’s also a great way to implement schema markup without having to change or add anything to the website source code. This makes it much easier to make changes to schema markup as new features come out of best practices change.
Google has detailed instructions on how to set up a Google Tag Manager container, and getting started with your first tags, variables and triggers.