How a Modern 4-Cycle Works

Perhaps the most common application of the Otto Cycle today is in the modern automobile engine.
This picture on the left depicts the 4 phases of a generalized 4-stroke engine.
The 1st phase, called the intake phase, is when the piston moving downwards pulls in the mixture of fuel and air used to combust.

In the compression phase, the piston moves upward in the sealed combustion chamber, compressing the fuel/air mixture.
In the 3rd phase, more commonly known as the "power stroke", is when the spark plug ignites the fuel/air mixture just as the piston continues reaches the top of its 2nd turn and continues downward.
In the exhaust stroke, the exhaust valve is opened, allowing the piston to push out the the used fuel through to the exhaust port.