The example video I have embedded below goes through the process of creating a teacher account (Google account) as well as using Google Classroom to import your class(es).
If you select Teachers, start here, then select Continue with Google, and then you can add your class. If you do not see the option, select your name in the upper right and then select Coach Dashboard.
When ready select Add new class and a pop-up window will appear. If using Google Classroom make sure to select the Import from Google Classroom button and then select your class.
Once you have selected your class, select the grade (you can skip this but I think you will want to select it), then you can assign the content you would like to.
Make sure to check out the tabs across the top for Content, Assignments, Progress, Activity, Roster, and Settings.
Embedded below is a 1 minute and 53 second YouTube tutorial I created.