Generally, you buy a domain name from a registrar, such as namecheap.com, then add a host record that points to your server.
Grabbing avatars from an external URL
I'd like to know if there exists a method to alter the way how avatars are automatically assigned to users (like Gravatar). For example, let's say I have an user named Foo and his avatar is located on a remote server & domain, on the URL domain.com/avatar/Foo.png. Basically, all I need is that NodeBB would automatically take the avatar from a specified URL and assign it as the user's avatar when he/she registers for the first time.
has been answered recently here
@markkus Extending change picture inside profile to allow a URL would be a nice addition for this.