NAV hold is for the ILS approach but be wary, on the very accurate panels it sometimes stands for autoland.
To do an ILS approach, you have to be alligned with the runway, and you have to have the frequency of the runway in NAV 1 (in the radio stack). There will be 2 purple needles that will guide you to the runway, 1 going up and down, thats for maintaining the glideslope, if its going down, you are too high, if its going up you are too low. the other one is going right and left, this one is to be aligned with the runway, if its going left, turn left a bit, its going right, turn right a bit. When you're at 300 ft. you shut down the autopilot and land manually.
APR switch is a kind of shitty autoland, it will hold the glideslope and runway heading for you but dont think of landing the plane with that switch on, you are going to smash the plane on the ground. I dont recommand on using it.
Hope this helps