Asked to be a McKenzie Friend – what do I do?

I have been asked to act as a McKenzie Friend. Apparently this is just the kind of thing that looks great on applications, but what can I actually do?

A friend of mine has asked if I would attend a hearing as a McKenzie Friend. I am a law student, I really want to help and I think this would be brilliant for any future legal career, but I really don’t know where to start. For example, does he have to make an application or do I just turn up? Any does and don’ts?