A celica has 4 cylinders, each of which work on a 4 stroke cycle. Intake
, Compression, Combustion, Exhaust. Picture the piston in the cylinder starting at top dead center. When it drop downs by means of the crankshaft it pulls air and fuel in, when it goes back up to the top it compresses the air and fuel. A spark plug ignites this air and fuel thus pushing the piston back down with great force. this in turn makes power that goes through the connecting rod, to the crankshaft, and through the drivetrain to the wheels thus making power. learn more on howstuffworks.com. they are installed usually on the top, or the side of the motor and have spark plug wire connected to them. and the kind you get does make a difference depending on how hot the spark is. hope this helps.