Creating a Facebook ID, formally known as a username, helps you spread the word about your profile on the social networking site. The managers of Facebook pages are also allowed to create a username. While all people are permitted to make a profile, only the official representative of an organization can start a page and assign it a username.
Creating a unique Facebook ID, or username, makes it easier for other people to point their Internet browsers right to your profile page. Your username appears at the end of your profile's URL, and another Facebook user who is signed in and types the URL into his browser is directed to your profile. For instance, if your username is "JSmith," your Facebook URL is "facebook.com/JSmith." Typing that URL into any Internet browser will pull up your profile.
You must be signed in to your Facebook account to create a Facebook ID. Go to the "Account" link in the top-right corner of your screen, and click "Account Settings" in the menu. Click on the "Edit" link in the "Username" group, and type your desired ID into the field provided. Click "Check Availability" to see whether or not the username has already been claimed by another user. Once you find an available username, click "Confirm" to choose it.
Each Facebook user is only allowed to change her username once for the life of her account. Bear that in mind when you create your Facebook ID -- using the name of your new boyfriend or a song you might hate later probably isn't the best idea. Also check your spelling when you create your username, as even a spelling correction is considered a username change. If you want to change your username again after you make your one allowed change, you will have to completely close your account and start anew.
Anyone with a Facebook account will be able to see your Facebook username, even if they are not permitted to see your full profile. In addition to appearing in the URL field above your profile, your Facebook username is always visible in your "Contact Information" section, and cannot be hidden. The only way to stop someone from seeing your username is to block her, in which case you completely disappear from her view on Facebook.