Refer to figure.
The reciprocating engine consists basically of a cylinder that is closed at one end, a piston that slides up and down inside the cylinder, and a connecting rod and crank by which reciprocating movement at the piston is converted to rotary movement of the crankshaft. In the closed end of the cylinder, known as the 'Cylinder Head', are inlet and exhaust valves and a sparking plug

Do not confuse it with the camshaft which is a shaft containing several attached disks of irregular shape that operate the intake and exhaust valves. It is driven at half the crankshaft speed as each valve only requires opening once per working cycle → once every two revolutions of the crankshaft.