the canister is a charcoal canister that is used to ''store'' gas fumes from the fuel tank and lines. as stated, it will release the fumes into the intake whern the conditions are right to do so.
the canister, 90 - 97, is located under thge hood next to the ABS pump if you have one. around 98 they moved the canister to the right rear, under body behind the wheel; opposite the muffler.
if you don't have one under the hood, you have one in the rear, or you have a CEL.