The charcoal canister is part of the Evaporative Emission Control System. This system prevents the escape of raw gasoline vapors from the fuel tank and carburetor.
The charcoal canister is designed to absorb fuel vapors under certain conditions. For a more detailed description, see Driveability & Emissions Controls of this repair guide.
The canister is a coffee can-sized object located in the engine compartment. Label the hoses leading to the canister before disconnecting them, then, remove the old canister from its mounting bracket and discard it. Install the new canister and connect the hoses as before.
The canister does not require periodic replacement. The entire system requires a careful operational check with a vacuum gauge at 60,000 miles. See Driveability & Emissions Controls for testing procedures.