google tag manager

Google Tag Manager (GTM) is a container script that serves multiple scripts (or "tags") at the same time.

marketing tracking. Mainly used by marketers to know from which campaign user comes from. Track user behaviour.

Previously if you ran facebook ad, you would need to add a 'pixel' to your site to track if user came from a specific facebook ad. Similarly if you ran a bing ads campaign you would need to add the custom code on all your pages. Tag manager lets you add a single script and the custom code is imported once via the tag manager script. everything is handled on the tag manager GUI. all types of tags and triggers.

Even if you dont plan to run ads it is still useful to collect users data by adding the google ads tag and the facebook ads pixel(tag) in your site bc later on you can run a remarketing campaign, and run ads to all the ppl the visited your site.

un trigger funciona para varios tags.
un trigger activa una accion, puede ser presionar un boton

un tag puede ser de facebook, pinterest, google ads, bing ads,...
tag de GA envia un evento a GA

Tag coverage is a report from a robot that crawls your site and in every page checks if the GTM script is present.

You might see issues in the report bc the crawler can't log in into your app. It sees the login page instead of the pages in your app. It also sees duplicates (/users/123 and /users/456)
you can ignore this warnings if your site correctly inserts the script, you can check by installing the Tag Assistant Chrome extension and navigating your site. To fix this issues