Intersections are formed by intersecting radials from two different VORs or by a VOR radial/DME distance combination.
Fixes on the other hand are just arbitrarily chosen points to be used by RNAV capable aircraft.
An ADF (Advanced Direction Finder) is the equipment used to receive an NDB (Non-Directional Beacon). It basically shows the direction to fly to get to the NDB. If you are to fly a given NDB track, position yourself so that the ADF needle points to the required heading. This is made a lot easier if you have an RMI rather than a pure ADF, as the RMI (Radio-Magnetic Indicator) incorporates a directional gyro so you don't have to watch two different instruments.
I can higly recommend Tim's Air Navigation Simulator
to those who want to grasp navigation using radio beacons.
While many airspaces these days require RNAV capability, understanding radio beacon navigation is still a skill required to fly many procedures.
I thought I was doing good trying to avoid those airport hotels... and look at me now.