There are 3 steps to register:

  1. Fill out the form below
  2. Verify your email address using the email we send you
  3. Add a username to your account (in minecraft, use /addaccount and click the link)

Octain will never ask you for your minecraft password.

Make sure you read the terms and conditions. There isn't much to read and they aren't written in hard-to-understand language.