How to Use Google Multiple Sign In

source: http://www.wikihow.com/Use-Google-Multiple-Sign-In

Google has a new feature that enables you to sign in to multiple accounts at the same time on the same browser. One of the benefits of this is that it allows you to read messages from several Gmail accounts just by opening up new tabs in the same browser.

[1]
Go to your Google Accounts page: https://www.google.com/accounts/ManageAccount

[2]
Click your name or email address at the top of the page.

[3]
Select Add account from the drop-down menu.

[4]
On the page that opens, enter the email address and password for another account you wish to access, and click Sign in.

[5]
Switch between accounts

[6]
Note that your default account becomes the first account that you sign in to. This means that when you sign into non-Google products unable to support Multiple Accounts, that your sign-in will be done via your default account.

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more sources

https://support.google.com/mail/answer/1721977?hl=en

http://www.pcworld.com/article/241719/how_to_log_in_to_multiple_gmail_accounts_at_once.html

http://gmailblog.blogspot.com/2010/08/access-two-gmail-accounts-at-once-in.html

http://www.cnet.com/how-to/how-to-sign-in-to-multiple-gmail-accounts-simultaneously/