A couple of weeks ago Facebook finally announced that they would allow users to pick out usernames. This helps to find and connect with each other very easily. Over 50 million users have them.
Today they introduced to log in to their Facebook accounts using their username rather than their email to log on to Facebook.com . Usernames are just easier to remember. It’s a common practice for many websites to allow users to log in with their username. It allows you to skip typing the extra characters.
If you don't have a Facebook username yet, you can choose one here
Go to "Settings" at the top-right of the Facebook page and then click on "Account Settings." The second option from the top is "Username." Press "Change" to enter in your new username and then click "Confirm" when you're ready to set it.
"Choose your new username carefully. You can only change your username once."