default FS2004 radio - need help using it.

I've had FS2004 for about 4 weeks now and I'm not sure what the various buttons on the default comm/nav radio stack are (on the 172, mooney, etc) Are there any good instructions on its use?

For example, buttons HD, APG, NAV, APR, REV, ALT, BFO, IDT..... In particular, the nav vs GPS syncs are a bit confusing to me.

Thanks, Happy New Year.

There are others who could explain this better, but I'll have a go at a few. Most of the buttons you mention relate to the Autopilot, and to the NAV radios (the ones you use to nagivate, not the ones you use to talk to ATC. Anyhow:

HD: When autopilot is engaged, this will hold you on a constant heading
APG: Not sure.
APR: Helps when you make an ILS (Instrument Landing System) landing, by keeping you at the right heading and descent rate. Read up on the excellent "Approach Guides" sticky post for much more on this.
REV: Not sure.
ALT: Will attempt to jold the aircraft at the altitude you specify, if autopilot is enagaged.

NAV vs GPS is something you should look through FS9's Learning Center to learn more about. It seriously affects instrument navigation, determining whether your direction is controlled by ground-based beacons or sattelite beams.

Hope someone else can offer you more helpful info