Mastodon is different from most online services. It is a federated network, so when you set up an account you need to choose a server to use. Your username then becomes a combination of your handle and that server you signed up to. For example, I am currently @
[email protected] what if you want to personalize that a bit more? What if you wanted to use your own domain for your Mastodon account without having to host a whole Mastodon server?.