The RT practical is an imaginary flight where they give you scenarios and you have to make the right calls. E.g. you are flying along and (the man tells you) you see a life raft down below, so you are supposed to make a Pan call and report its position (or a Mayday??). Later (the man tells you) you get a fuel leak, so you are supposed to tell ATC you are diverting to some other place.
The bit I found hard was knowing when to make calls because the exam is much faster than the flight could possibly be, so by the time you finished one call you have travelled 100 miles and they are after the next one
It's pretty easy if you know the call formats.