Can someone explain to me what this actually does and is there a correct way to clean it or do i replace it every so often?

 

It absorbs gas vapour when your engine is off, so they don't just evaporate into our air. And it shouldn't need cleaned, if it's working properly the absorbed vapours should get sucked into the intake when the engine is running.

 

Is there a way to check it and make sure it is working properly?

 

This is from the FSM, with the 2 upper ports facing you "A" is on the left, and "B" is on the right.

"Charcoal Canister
1) Disconnect hoses from charcoal canister. Check for clogged
filter and/or stuck check valve by applying low air pressure to port
"A". See Fig. 26. Ensure air flows freely from other ports on charcoal
canister.
2) Apply low air pressure to port "B". See Fig. 26. Ensure no
air flows from any other ports on charcoal canister. Replace charcoal
canister if defective.
3) To clean charcoal canister filter, apply 43 psi (3 kg/cm  )
air pressure to port "A" while holding port "B" closed. Ensure no
activated carbon comes out of charcoal canister. DO NOT attempt to
wash out charcoal canister."