1990 Toyota Camry car is 4 cylinder but runs in 3 cyl

A first step when buying a car with high mileage is to do a tune up. Replacing spark plugs and ignition wires would be the first step. Or if on a budget you can check which cylinder is not working and try to fix a possible loose wire or clean dirty spark plug. I wouldn't drive on 3 cylinders though, it shoots unburned gas into the exhaust which is not good for the exhaust or you since it can explode.