Sign in to your account and click my account link in the top right-hand side of the dashboard, and then click on my account link (or the users link) to be taken to the account section.
click the 'users' button in the account navigation section.
Your current user list will be shown as per screenshot below:-
To add a user click on the 'add new user' button, you will then be prompted to provide user details. Once the details have been entered click 'create new user' and instructions will be sent to that new users email address with how to complete their account setup.