Your teacher's Google Meet link will be posted in the banner at the top of your Google Classroom and in a button under the Classwork tab or in the Announcements Inbox in Seesaw. If your teacher has not started the Meet yet, you will see a message saying you cannot join. Try again after the teacher has started the Meet.
Google Classroom - Find your Meet link:
Seesaw - Find your Meet link:
If the teacher has not started the Meet yet, you could see this message: