whats this
 

on the drivers in the engine compartment by the head lights there is a cylinder about 5in accrost what is this

I'm gonna take a shot...

Your charcoal canister?

sounds right to me.

what the hell is the charcoal canister and what purpose does it serve?

whats this
 

It's basically for emissions.

It takes the gas vapors from the gas tank instead of putting them out into the atmosphere. It stores them until the engine is turned on, then it sucks the vapors into the throttle body.