Alot of it is confidence and working out what you are going to say before pressing the transmit button. Remember - ATC are there to help YOU, so ask for what you want!
Well done for doing such good prep before your test.
And yes, alot of it IS confusing! I've been flying for years, I fly commercially and yet even I couldn't tell you exactly what services FIS RAS or RIS can provide - I am sure there are lots that I don't know about.
Good luck for Tuesday!