Charcoal should be stored in a cool and dry space with the bag clipped closed. Store charcoal away from interior walls that have been sheet-rocked, and away from combustible materials like gasoline, oil and rags. If you have a charcoal bucket, or a covered metal bucket, this is a great place to store your unused charcoal. Always follow the packaging instructions.
When you are done cooking with charcoal, you can douse the burning coals by slowly and carefully pouring water or sand over them, then allow both the barbecue and coals to cool off completely. You should not use a hose of any sort for this as you can send charcoal, that is still hot, flying. When everything is cool you can dispose of your ashes into a metal trash can or bucket. Check with your local government about disposal of these materials, as it may differ from place to place.