VOR and TacAN are radio beacons that transmit a pattern of radials that are orientated to magnetic North at the transmitter. Those signals are received by the equipment on the aircraft or ship and indicate the magnetic redial. To plot that reading on a chart you still need to correct for the magnetic variation at that location - the difference between true North and magnetic North. A non-directional beacon (NDB or ADF) transmits a signal which has no directional orientation - think of an AM radio station. The equipment on the ship or aircraft reads the magnetic bearing from the location of the ship or aircraft. To plot on a chart the magnetic variation at the receiving ship or aircraft is applied. The same applies to taking a bearing by radar or visually.
Hope this helps.