Verified 06/14/2022
If you signed in to Google on a public wifi (RISKY!) but forgot to sign out before leaving or if you've gotten notification that there's been a login that wasn't you, there's a way to see all open sessions of your email and to close them.
Open your email from a computer (not from your mobile device.) Click the tiny Details link at the bottom right hand side of your inbox.
You can look at the details of each open session. If there's one from a location or device that you don't recognize, click on Sign out all other web sessions.
If necessary, you might want to consider changing your password.