The idea of a smoker is to use indirect heat that generates smoke. The heat, such as charcoal, hardwood, gas, or a combination, is offset and away from the food. In some rigs it is in a separate firebox off to the side. In a water smoker, it is located at the bottom of a tall unit with a water pan in between the heat and the food.
When smoking, you use a temperature of around 225 degrees for a long period of time. This low and slow cook time allows tougher cuts of meat to break down and become tender. Good examples are a Boston Butt roast, Picnic Shoulder, Pork Spare Ribs, Beef Brisket, Beef Spare Ribs, or any other cheap and tough cut of meat that you want to make flavorful and tender.
There are other meats that are not tough that benefit from smoking due to the additional flavor such as Beer Can Chicken, Pork Chops, Cornish Hens, Meatloaf, Salmon, and many others.
You can accomplish the same tenderizing aspect of low and slow cooking in your oven. Simply set the oven to 225 degrees and put your meat in a covered roasting pan, aluminum foil, or directly on the rack over a drip pan. The only difference in using the oven is you don’t get the smoke flavor from burning wood.
You can also use a regular gas grill or a large kettle style grill for smoking. You just keep the heat on one side of the grill by banking the coals to the side or only turning on one burner, and then put your meat on the other side. You can put a drip pan under the meat and add wood either directly or in a firebox or aluminum foil to the heat source.