Your google classroom page looks like this
Announcements from your teachers will appear hear.
When it is time for your live lesson a google meet link will appear and you may press the link to enter the meeting.
If you arrive to the classroom early and the link is not there then try refreshing your page at the start time. For internet safety reasons the link will not appear until the time of your lesson.
If you are on an ipad or iphone there will not be a link. Instead a camera will appear at the top of the page when the lesson starts. Click the camera to enter the lesson.