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.

Some of the top reasons people have more than one Google account are: Having a personal and work account. Having a personal and school account. Having a personal, school, and work account (the trifecta)

See all settings. Click the Accounts and import tab. In the "Check mail from other accounts" section, click Add a mail account. Type the email address of the other account, then click Next. Make a selection and click Next.

On your computer, sign in to Google. On the top right, select your profile image or initial. On the menu, choose Add account. Follow the instructions to sign in to the account you want to use.