What are the differences between VORTAC's and NDB's?
The VORTAC indicator in the cockpit tells you which radial line connects your current location with the ground station you are tuned to in degrees referenced to local magnetic or true north. NDB broadcasts a signal which contains no direction information; the NDB indicator needle in your cockpit only tells you how many degrees left or right you must turn your plane to follow a line leading to the ground station you are tuned to.
If the VOR transmitter on the ground contains a transponder and your receiver is appropriately equipped to send that transponder a signal, the VOR system can also tell you how many miles away from the ground station you are in addition to which radial you are on. this is called DME, for Distance Measuring Equipment. NDB systems cannot do this for you. VORTAC (VOR + TACAN) always have DME equipment.