You can join a class video meeting after the teacher starts the meeting.
To use Meet, sign in to Classroom with a school account. Your account looks like studentlogin@stisidore.org
  1. Go to classroom.google.com.
  2. Click the class.
  3. Choose an option:
    • On the Stream page, at the top, click the Meet link.
    • On the Classwork page, at the top, click Meet Add video meeting.
      Click Meet link
    • On an announcement or post, click the link for the class video meeting.
  4. (Optional) To allow Meet to use your camera and microphone, click Allow.
  5. In Meet, at the top, make sure you’re signed in with your school account. To switch accounts, click Switch accountand thenselect the Classroom account.
  6. To join the class video meeting, click Join now.


Adapted from: https://support.google.com/edu/classroom/answer/9777280