Users can create a unique username for their accounts in order to maintain a consistent user identity. Usernames are super useful identifiers you can give to people you want to connect with. You can also pay with $usernames between each other.
Here is the introduction to how to create the username.
1. Click on the profile
2. Click the arrow on top of the profile page
3.Click on the username to edit
4.Users have only one chance to create a unique username for their account