What happens when you put gas in 2 stroke dirt bike engine?

The engine cycle of a 2-stroke is as the name suggests comprised of two strokes of its piston.

In its most basic form a two stroke engine operates by drawing an air-fuel mixture into the crankcase. As the piston descends it uncovers two ports in the cylinder walls. A new charge (volume of air-fuel mixture) is forced into the combustion chamber by the descending piston through the intake port. The new charge itself forces out the gases of the previous spent charge.

After the piston passes bottom dead centre and rises it covers up the ports again, sealing the combustion chamber and compresses the charge. When the piston passes top dead centre, the charge is ignited. The piston is forced down and the process is repeated.