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Go to https://www.gmail.com/ in your computer's web browser. In the text field that appears, type in your Gmail email address. It's below the text box. Type in the password you use to log into your Gmail account. It's below the password text box. If asked to enter a two-factor authentication code, do the following:  Retrieve the two-factor authentication code from your phone's Messages app. Type the code into the Gmail text field. Click Next. This should take only a few seconds. If you want to sign into another Gmail account without signing out of your current one, do the following:  Click your Gmail profile icon in the top-right corner of the inbox. Click Add account at the bottom of the drop-down menu. Enter your account's email address and password.
Open the Gmail login site. Enter your Gmail email address. Click Next. Enter your Gmail account password. Click Next. Enter your two-factor authentication code if prompted. Wait for your Gmail inbox to load. Add an account.