If you have an account created on another site by Mediocre, you may use it here. If you don’t, you can create a new account and pick a username.
In the past, sites operated by Mediocre allowed use of native account login (by email) or third party authentication providers (Amazon, Facebook, Google). As covered here, Facebook will be the sole third party provider moving forward.
Note: if you’re here early, Mediocritee may not have Facebook authentication enabled yet. If you sign in to Mediocre sites using Facebook, simply click the “I forgot my password” link to get a new password. See that same thread for more.