Facebook lets you set your ID to anything you choose, if it is not already claimed by another Facebook user. This creates a unique URL for your Facebook profile in the form of "facebook.com/johndoe" -- that makes it easy to share with others. Rather than search for you on Facebook, your friends and family can simply type your Facebook profile URL into a browser's address bar. You can change your unique Facebook ID only once.
Sign into your Facebook account at facebook.com.
Type "facebook.com/username" (without the quotes) into the address bar of your browser, then press "Enter."
Type a desired ID into the box and click "Check Availability." The username must contain only alphanumeric characters (at least five). Alternatively, click a username Facebook suggests based on your real name.
Click "Confirm" if Facebook notifies you that the ID you typed is available. If the ID is not available, enter a different one and click "Confirm" until you discover one that is available.
Make your Facebook ID easy to remember, if possible. That way you can easily direct your friends to the URL.