Yes the heading clears it all, you can now loging to your facebook account just by entering your username in place of your e-mail address. The best thing about this feature is that it is not only for facebook.com web browsers but also for m.facebook.com from your mobile and any website that suports facebook connect.

Let us clear you one thing that you can use your user name in place of your e-mail, it’s not your name. Top find your username you can go to,

Settings >> Account Settings

or simply use this link. You can find your username there.

Login:

Please remember that is is an additional feature, you can also use your e-mail to log in as we do usually. Below are the two screen shot for logging in using your username. Note that we are entering our username in the space which is given for e-mail.

SOURCE: facebook official blog