Tag Manager is like a box where you can store pieces of code and distribute them to your site or app. A piece of code is called a tag, and it can do things like collecting data, installing third-party tools, changing the look of your site or app and much more. Tags don’t run all the time, but only when triggers tell them to do that. For example, an all-page-view trigger tells the tag to run on all page views. Tags and triggers also use information holders called variables to change some elements of the code.
In short, a tag is a code, a trigger is a signal, and a variable is a piece of information.
Tag Manager can access your site or app after you install our container. We ask you to install it on all pages on your site or app because only then Tag Manager can reach these pages. When you set a tag and publish it, Tag Manager will use this container to run a tag on your site or app.