Hey
Keep an eye on your university portal/website, they will publish any opportunities on there, its usually an application and interview.
It not a difficult to become one at all. they usually look for skills like communications, presentations and being friendly and approachable, as far you can display these sort of skills you will be good to go.
Pay varies depending on where your university is located. But, most university will pay between £8 - £12 per hour, so your earnings will depend on how much you work. The more you work the more you'll earn.
Hope this helps, let us know if you have any other questions.
Arsh Shaikh
BA Financial Economics
Coventry University - Campus