When someone tries to explain to you what exactly goes on in a car engine you probably won't understand much. The video below shows you the full process.
Intake
The valve on the right opens and fuel (+air) fills the cylinder
Compression
While the piston goes up it compresses the fuel mixture
Ignition
When the fuel is compressed the spark plug lights a... spark to ignit the fuel. This pushes the piston back down.
Exhaust
The valve on the left opens to let the "smoke" get out and free space for the next cycle