Some people make do with the same email address for life, but for others we have a few emails set up for different purposes, such as work, PayPal and social networking. However, isn’t this a problem when it comes to logging in and out? Not any longer as Gmail users can stay logged in to multiple accounts, switching between accounts is a matter of clicking on the name at the top and selecting the right account to use!
This is what you need to do in order to get started;
Go to the Google multiple sign-in setup page and select “On” then check each checkbox and click “Save”
Now that has been done go to Gmail and log in and select “Sign in to another account”
Enter your details for the next Google account, click, “Sign in” and repeat for all accounts!
Now you are done, switching between accounts is a matter of clicking on the username in the top right and selecting the right account.
Source [PC World]