That is your crankset. The crank arms are what the pedals attach to. The Chainring is the large cog that turns the chain.

You have an older crankset with cotter pins to hold the crank arm in place. But this one has a bolt hammered in there. This is not a good idea. New cotter pins can be purchased.

Removing this bolt can be done. There is a tool to remove cotter pins. Some people use a punch and a hammer but you must be careful not to damage the surface of the metal that the cotter pin touches.

good luck.