Well, first remember that you can communicate both by text and, if you have a mike, VOX (voice). Go to the AH Trainer's site
here and look down the left column. You'll find "The Radio" there and it has all the details.
To quickly get you going do this: For text, just hit backslash "/" to call up your text window then select the appropriate text channels using the dropdowns. You'll want Country and Room text channels selected and then the other two as needed. There are two VOX channels, Range and Channel. Range is always available and it let's you talk on VOX to those that are within Icon range of you by hitting the "F12" key. You can tune Channel to whatever you want and transmit by hitting "T". If you join a squadron they'll have a standard channel that everyone's on. To tune the Channel frequency type in ".radio 5 XXX" then hit enter. XXX is the frequency you want such as 101.