If you have already joined Facebook, and you have signed out, and you have no idea how to get back again, just type this address into your address line "http://www.facebook.com". You will be presented with this page:|
If you have previously joined, once you fill in your email and password on the upper right, you'll find yourself on your "news feed" page. If you were still signed in when you typed in the Facebook address, you will automatically be sent to your "news feed" page, or perhaps to the page you were on when you last left Facebook. Of course, if you have NEVER joined, you will need to fill out that entire block of information to get yourself signed up.
Whenever you are signed in to Facebook you will see this bar at the top of the page:
Go back to the Become a Fan page, here.