Once you get a Facebook account, it will include to pieces of information that uniquely identify you, namely an email address of your choice (that you own, of course), and a password. As you saw in the Facebook sign in tutorial, the only way to access your profile if you are currently logged out is to supply these credentials and click on the "Login" button. But what happens behind the scenes as soon as you do? This tutorial explains the Facebook login process as it happens in the background: this will help you understand how to sign in to your account based on each situation (e.g., how to login to Facebook when you are not using your own computer), like the secure Facebook login option (HTTPS).
As mentioned earlier, you cannot login to Facebook without supplying at least an email address and password: once you have, and either click on "Login" or hit Enter / Return, the information you entered (which is called "credentials") will be sent to Facebook's servers for "authentication" - this is the technical name of the process that consists of checking a set of credentials against the database of existing users.
At that point, one of two scenarios will unfold: if you mistyped your email address and/or password, Facebook will come back with an invalid login screen, which asks you to "Re-enter your password" (as mentioned in "Facebook login and sign in settings", this message does not specify whether the login problem came from the email address or the password itself, so you should check both!
Short of proceeding to reset or change your account password, you will just need to carefully retype this information inside the secondary sign in form, and try to login once more.
You will know when you successfully logged into your Facebook account once you see your profile homepage - this means that you were authenticated without any problem. What happens behind the scenes if you checked the "Keep me logged in" of the sign in form is explained below.
A very convenient option Facebook includes in the sign in form is the "Keep me logged in" checkbox, or "Remember me" option. Just like Hotmail Sign in and other online forms that collect credentials, you can make Facebook automatically sign in to your account with a simple click to enable this setting.
With this option enabled, you will remain signed in to Facebook until the cookie expires, or until you manually clear your cookies. For the meantime, whenever you access another Facebook profile or the Facebook homepage, you will automatically be logged in as yourself! (Note that you should not use this option from a computer accessed by others, unless you really trust them and their sense of humor!)