What’s the difference between logging in and signing up?

If you don’t have a Facebook account, you can sign up for one in a few easy steps. To sign up for a brand new account, enter your name, birthday, gender, and email address into the form on http://www.facebook.com. Then pick a password.

Log in
If you already have a Facebook account, you can log in to your account from the same page. Just enter your email address and password into the section at the top of the page and click Log In.