Assuming you are referring to the common aerosolized whipped cream canister, here is how you use it:
1. Make sure the nozzle is screwed on tightly.
2. Invert the can and dispense a small amount of whipped cream into your bowl or onto your spoon.
3. Return the can to its upright position.
4. To clean, unscrew the nozzle and run warm water through it.