A teacher can directly add a student to a class, or give them the class code to join themselves. The following instructions are from the point of view of a student in Classroom.

To add yourself to a class with a course code:

1. Sign in to Classroom at classroom.google.com.
2. On the Home page, click the + icon.
3. Enter the code that the teacher gave you in the box, and click Join.

The class stream will open. If your teacher has added an overview, you can read it by clicking About near the top of the page.