1. Open the 'People' tab. Click on the 'add person' symbol on the Students line.
2. Type in the email address(es) you want to share the classroom with and click 'Invite'. After each email address, press the Enter key.
3. On the People tab, you will see the student(s) invited. Similarly, you could invite another teacher to share the classroom.
4. The student(s) will receive an email inviting them to join the class. They need to click JOIN.
5. They click JOIN again (assuming they are signed in under the correct account - click Switch Account if not).
6. They are taken to the class.
7. On the People tab, you will see that once they have joined, the 'invited' note is removed.
Note, it's also possible to share a class with another teacher.