FB Usernames & ID usage: How are usernames and user IDs used on Facebook profiles?

FB Usernames & ID usage: How are usernames and user IDs used on Facebook profiles?- Usernames and user IDs are part of your public profile, which can help your friends find you on Facebook.

See: How do I add a family member to my About page?

Username on Facebook

Your username is often a variation of your name, like jane.doe33 or janedoe3. You can create your own username or choose a username that Facebook suggests. Some of the things you can do with usernames:
Create a custom link (for example, www.facebook.com/janedoe3) to your profile that you can share with your friends or post on external websites.
Access information about someone through Facebook. For example, if your username is janedoe3, your friends can go to “facebook.com/janedoe3” to see your profile and any public information.


You can control what information you share publicly. 

Facebook User ID

Your User ID is a string of numbers that doesn't personally identify you but does connect to your Facebook profile. You have a User ID automatically, whether or not you choose to create a username.

The Facebook User IDs can:

• Allow someone with the ID to see your profile, including any public information. 
• Help other applications personalize your experience by connecting with your Facebook account. When you allow apps to connect with your Facebook account, they can use your user ID to see public information, like your public profile and your friend list. 
• When you run into issues with an app or game, your User ID can help the developer better investigate the problem to understand and address your specific concerns.