Introduction to Google Tag Manager
This short video will give you a 101 introduction to Google Tag Manager: https://www.google.com/analytics/tag-manager/
The core, “101” benefits of Google Tag Manager are related to speed in two different ways: 1) It keeps your tracking codes loading asynchronously so that they don't “block” the loading of your text and images on your site and 2) It makes it more “marketer friendly” to load new pieces of code on your site — rather than having to get in-touch with your web developer or IT department every time you want to add a new piece of code to your site.
There are additional benefits to using Google Tag Manager such as advanced analytics tracking, but this video just covers the 101 benefits of GTM and a brief walk-through of how to use tags and triggers in GTM.