Creating a user account means that you supply a username (your real name or a nickname) and a password. The system will reject a username that is already in use. A user account is created only once. You are then "logged in". The next time you log in, you supply your username again and demonstrate with the password that you are the same person. (Use caution if sharing your password with other people; this could allow them to misuse your account, which could lead to the account being blocked.)
Edits you make are recorded under your username.