I was there once as well
Simple stuff: Callsigns ending in "Radio" or "Information" don't give clearances. They may be able to get you one (via the telephone etc.), but the person you are speaking to can't give one. Those called "Tower", "Approach", "Control", "Radar", "Director" are able to give you clearances, but normally only through their "Manor". To get a clearance, just ask for one. If they can't supply, they'll know someone who can and will normally pass you on to that person or get it for you. And when they supply it, read it back. What do you call them on first contact? Their full name should be on the piece of paper with the frequency on. All can give FIS, but it's the last four above who give you the RIS/RAS and Control (if that is a service).
Have fun.