Google Tag Manager or GTM is a library/tool that will help you keep your sanity by managing your applications scripts and tags.
If you've ever worked with Google or Facebook Ads, you know that it requires you to add a bunch of tags to your app. Then, say that you want to add another tracking service... You now have another 3rd party library that you need to include in the footer of your app. After awhile this is going to cause a cluster-fuck in your application. You'll have script tags and iframe embeds all over the place.
Wouldn't it be amazing if all these 3rd party scripts and embeds could be managed in one place? That's what Google Tag Manager is here to do.
Google Tag Manager is a great tool where you can add new users, with limited access, and allow them to add any libraries or scripts to your app. It is very common for a marketing department to have control of adding new Pixel tracking or User tracking scripts in the app. And now they won't have to request a developer every time they need something new added.
Another cool thing about GTM is that you can automatically create triggers for when a user clicks a button or enters text in a text box. This will allow you get get some great analytics data about elements and user interaction on your site.
Be sure to sign up for Google Tag Manager, it'll make your dev life much easier ;)