Step 2: Two Stroke Theory
Here is the process of the engine.
Intake, The fuel/air mixture is first drawn into the crankcase by the vacuum created during the upward stroke of the piston. The illustrated engine features a poppet intake valve, however many engines use a rotary value incorporated into the crankshaft. During the downward stroke the poppet valve is forced closed by the increased crankcase pressure. The fuel mixture is then compressed in the crankcase during the remainder of the stroke.
Transfer/Exhaust. Toward the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder. Unfortunately, some of the fresh fuel mixture is usually expelled as well. I'm going to interrupt here for a second to explain how that fresh mixture is prevented from being expelled.
so, you think an exhaust pipe is just meant to get the exhaust away from the engine, right? well in the 4 stroke application that's completely true, but in the two stroke, you must use a specially formed pipe, that uses something called backpressure, to force the expelled mixture back into the combustion chamber, this can be seen in the animation quite clearly.
Compression. The piston then rises, driven by flywheel momentum, and compresses the fuel mixture, insuring that the mixture explodes properly. (At the same time, another intake stroke is happening beneath the piston).
Power. At the top of the stroke the spark plug ignites the fuel mixture. The burning fuel expands, driving the piston downward, to complete the cycle.