I am trying to gain an understanding of how the radio systems in the aircraft work in FS. How does the airfields (ATC) communicate with the aircrafts and AI?

Is there any tutorials or reading I can do to understand
how this works and how to create it?

Wish_bear ???

Thanks for that- but I know how to turn on the ATC,
I wanted to understand how it works.

How does the ATC communicate with the aircraft, how does it know the call sign, is there a ATC config file?
Are there TACAMs? What does the aircraft ping to, to find its location and know what to dial into the radio nav and com gauges....where is that all programmed in.
Is it a file you can look at and add to or make changes to?

wish_bear

The callsign and other information about your aircraft is in the aircraft.cfg file. Here's an example from my 747.  Yours will probably look different.

[fltsim.0]
title=Boeing 747-400 Global
sim=Boeing747-400
model=
panel=
sound=
texture=
kb_checklists=Boeing747-400_check
kb_reference=Boeing747-400_ref
atc_id=N700MS
atc_airline=Global Freightways
atc_flight_number=1123
atc_heavy=1
ui_manufacturer=Boeing
ui_type=747-400
ui_variation=Global Freightways ...

[General]
atc_type=BOEING
atc_model=B744

Anything with 'atc' before it is what ATC will call you.  In this example my tail number is N700MS, ATC will call me "Global 1123 heavy" (heavy being a big jet - set this to 0 to leave this off) when it is talking to me.  It will call me Boeing 747 when it it talking to someone else about me.

There are a lot of predefined "types" and "models".  If you get a wierd plane it may come pre-programmed or you can look up a close match in the list.  Send me an email and I'll send you a document with most of the types and models (34k zipped).

When you contact ATC (`) they will you to "squawk" (set your transponder or xponder) to a certain frequency.  The ATC comminucation box will offer to do this for you, then they will confirm that they have radar contact with you.

Tuning in to the NAVigation and COMmunication frequencies is a little trickier but you can get most of them from map mode (the button that looks like a compass).  I use FSNavigator so I don't look at the map much.

I agree.  I wasn't going to write an entire tutorial on navigation and communication.  Wish_bear has built in lessons for that, and here's a site with some good resources http://www.emeraldair.net/training.html .