The Tracking Code is essential to analyze user behavior on your website and catch all the fraudsters that come your way.
The code can be added through Google Tag Manager, as you would any other piece of code. The Tracking Code is the same script for all accounts.
The Tracking Code can be found under Domain Settings > Domain Tracking Setup > > Tracking Code.
Important: Google Tag Manager (GTM) requires previous installation of GTM code on your website in order to be able to apply changes to your domain. The installation steps are very simple and shown when you first sign up to GTM.
Details on how to add a new Custom Tag in GTM can be found on Googles Tag manager help page.