There are two ways for users to become registered in Compass. One is that they do it themselves, and the other is that someone does it for them. Information on self-registration is here, and information for people with Administrator, HoD, and Superuser access on how to register someone else is given below.
From your department homepage, select the Staff tab and click the Add new staff button to open the form. You will need to know the name and username (eg: abcd123) in order to complete the process.
Open your admin toolkit, and choose the Add new person button to open the form.
Since people can register themselves easily, if you know of someone who needs access, please just ask them to do it themselves.