I've been wanting to learn VOR navigation for a while now, because it seems to make a simple flight alot more satisfying.
But anyway, I took the lesson the game provides about it, but to be honest, it's quite terrible, and hasn't made anything clearer.
The main question(s) I have is:
-How do I get the frequencies for the NAV radio?
-Where do I get the ADF frequency from?
The answer to both questions is on the map(Map mode), click on the VOR or NDB in question for frequencies.
This may interest you also: http://www.navfltsm.addr.com/index.htm
If you're trying to do it realistically you can get an old copy of a sectional map. You'll find all the navaids in an area on the sectional. Have a look at the map legend for details on how the VORs and NDBs are labeled. You're taught to dial the frequency into the nav radio and then use the ident feature on the radio to compare the morse code signal against what's shown on the chart. That's to ensure you've dialed in the right VOR.
Real maps and AFDs (airport facility directories) are great! Back in the day, you could get outdated ones free from a local airport.