On a classic it's easy. You start with the bench part, the part you put your rump on when you sit in the back. Put yourself in front of the seat. Place your hands about 1/4 of the way in from the side of the seat. There is a plug thing that sticks down from the bottom of the seat to anchor the front of it.
Grasp the front of the bench and lift up firmly to uplug the anchor thing. Go over to the other side of the seat about 1/4 of the way in from the other side. lift it too. Once the front is loose you unthread all the seatbelts from the rear and slide the whole thing sideways out of the car.
The seat back has four heavy wire loops sticking down from the bottom of it. Once the bench is out you can see them clearly. Unscrew the machine screw that holds each loop to the body of the car. Now the bottom of the back is loose. Up near the top of the back are four heavy wire hooks. (You can't see them yet). Lift the entire seatback up about two inches to disengage the hooks. Now the seatback is free and you can slide it sideways out of the car.
If you are going to have the pieces out for a while I would reccomend screwing all the machine screws back into their holes so you can find them when you want to put the seat back.
There are a variety of tubes and wires under the seat. Mind that you don't break any of them, they all probably do something. If you want to run more wires into the back of the car it is easy to work them into the trunk while the seat is out.