Go to http://accounts.google.com/signin/usernamerecovery and enter any email accounts or phone numbers that you've had for a while and which may have been used as recovery info. The “find your email” page can help you locate any forgotten Google accounts.

To sign in to your Google Account (or any Google product): Go to the sign in page of the product (for Google Accounts it is myaccount.google.com). Enter your Gmail username (everything that appears before '@gmail.com'). Enter your password.

Another way to find Gmail email address from the desktop website or the official Gmail app is to select your profile image at the top right. If you're on a computer, this shows the email account you're using right now and any other Google accounts you're logged in to in the current browser session.