There are two styles of barbecues; covered BBQs also known as Kettle barbecues, and uncovered barbecues.

Uncovered barbecues are the older style BBQ and they consist of a flat plate and/or a grill plate that you cook the food on, but there is no lid to cover the food while it is cooking.  These BBQs are generally cheaper in price than the covered BBQs.

Covered BBQs come with a hood that you can open and close, and many of them also come with an inbuilt thermometer on the hood that tells you the temperature of the oven that is created once you have the BBQ lid closed.  If you have a covered BBQ this means that you can use your BBQ as you would use an uncovered one, but you can also bake food using your BBQ.  This can be very handy!  I have even cooked entire Christmas roast lunches using a BBQ - this means no more slaving in a hot kitchen, and more time to chat and relax with guests while the food is cooking.  If you can afford to buy a covered BBQ I would highly recommend that you do so.