Firstly, you must register online via the Student Portal.
Head here to find out more about the first part of registration: gre.ac.uk/welcome/registration/online
If you are a new student, the University will then need to confirm certain documents to register you. Your qualifications will be checked online but your ID will need to be checked in-person. All international students will need to show a current valid and in-date passport.
Non-EU students must also show a relevant immigration document (this can be a stamped entry visa, a current visa, or BRP).
EU nationals must show either a relevant immigration document (as above) or evidence of settled or pre-settled status to the EU Settlement Scheme.
For all registration information, head to this webpage: gre.ac.uk/welcome/registration