Once the Google Meet session has started you can find the record button by clicking the 3 dots on the bottom right of the screen and selecting Record.
Click Start on the notice that pops up
To stop recording, follow the same instructions or end the meeting.
Where do my recordings go?
Recordings are saved by date in your Google Drive under My drive > Meet Recordings
It can take awhile for Google to process the video and upload it to your drive. You will get an email notification when the process is complete.