Hi
Ok this is as simple as I am.

VOR stands for Very high frequency Omni Ranging. And its exactly that it operates in the high freuquency bandwidth as you can tell when you tune you radio to a VOR frequency E.G. 111.1 Mhz (megahertz) thats high frequency. The signal can tell your instruments direction, height and ranging hense you can do an ILS approach.

NDB stands for Non-Directional Beacon. And again it does what it says on the packet. These operate in the low frequency range 190 to 535 Khz (kilohertz) and all it will allow you to do is home in on the beacon, that is fly in a straight line towards it.
So look at the airport where you want to land, tune the VOR frequency to NAV1 and hopefully you'll see a NDB beacon on the approach line to the airstrip(but not always), tune this to the ADF and the combination of the two will hopefully fly straight onto the airfield.

Note not all NDB's are on the approach vector and are offset. (Before I get any mail.)
Please note I'm a novice and the accuracy of information given is on the understanding it could be completely pants and I'm sure fellow Flight Sims will put me right if it is.

Happy Landings
Phil

Tower : Flight 2-0-9er, you're cleared for take off.
Oever : Roger!
Murdock : Huh?
Tower : L.A. departure frequency 1-2-3 point 9er.
Oever : Roger!
Murdock : Huh?
: Re-quest Vector, over!
Oever : What?