Ok, lots of questions, so I'm going to try and give you a comprehensive treatment of smoking foods.
First, smoking techniques can be used to enhance the flavor of meats, veggies, fish, and fruit. Each wood produces a slightly different flavor. The smoky flavor is caused by a deposition of smoke particles on any food. Those particles contain oils that distribute themselves over time into the food being smoked.
Smoke, in and of itself is normaly a bitter, pungeant flavor. But when it is applied in the right quantity, it loses its bitterness and belnds with the natural food flavors. It is usually combined with other flavors either during the cooking time, or by the application of finishing sauces or gravies.
When smoking meats, there are basically two types of smoking; hot and cold. Hot smoking is a technique where heat from the fire that produces the smoke also cooks the meat. This is the method used for foods like pork chops, beef brisket, Boston Butt, ribs, etc. The smoke penetrates the surface of the meat, staining it pink. This is called a "smoke ring" and is an indication that sufficient smoke oils have penetrated the meat to impart good flavor.
Cold smoking is a technique to infuse smoke flavor into cured meats such as country ham, bacon, many sausages, etc. The smoke fills the environment where the meat is kept, and has a low enough temperature that the meat remains raw. This is a technique that is used for foods like smoked salmon (which is eaten uncooked in many places), bacon, jerky (a dried, not cooked product), etc.
Fruits and veggies are hot-smoked.
Cold smoking is not usually done by home cooks as it can produce potentially dangerous pathogens in foods if not done properly.
You can hot-smoke in a variety of ways. Personally, I don't have a smoker, but achieve very good results on my Webber Kettle charcoal grill. I can get the indirect heat by seperating the charcoal into to piles, on opoosite sides of the grill, and laying soaked wood directly on top of the burning coals. The meat, or food to be smoked is placed in the middle, where no charcoal is under them. The wood protects the meat from intense infr-red radiation, and thus keeps the meat from scorching. Also, I control the temperture by adjusting the air vents. The less air I allow in, the less heat is produced.
Also, there are a few ways to decrease the time to get great smoked flavor. As was stated, smoking in the traditional way requires several hours of time, and a constant watching of the fire and wood. To decrease the required time, you can place tough meats in a pressure cooker to cook the meat, and then place it in a smoker to give it the smokey flavor you desire. I did this recently with pulled pork made from a Boston butt and it came out great. Everyone thought it had been cooked low & slow for hours. It cooked in a slow cooker, set on low, overnight whle I slept. Very little work for me. I then pulled the pork into shreds and put it into my heaviest cast iron pan and placed that on the grill, along with apple wood chunks. I stirred the meat after thirty minutes, and let it smoke for thirty more.
When smoking meats, it is important to ballance flavors. The end product must be a ballance between smokey, salty, and sweet flavors. Often times, a piece of meat in brined, marinated, or rubbed with a blend of sugars, spices, salt and herbs. In addition, many smokers use a "mop" to flavor the meat. This consists of a flavor mixture of water, salt, sugars, and herbs/spices that are brushed onto the meat periodically as it cooks.
You can also purchace indoor smokers, which are long, rectangular pans that have a lower and higher surface, with a tight fitting lid. The lower chaber is filled with either small wood chips or herbs. The upper chamber is where the food sits. Smoke from the bottom surounds the food and is held in the pan by the lid.
As for flavor, you just have to try different woods. I like fruit woods for pork, fruit woods, mesquite, maple, and birch for beef and poultry. I use hickory or cedar for fish. There are many other woods that are available, depending on your location. Some of these are walnut, pecan, peach, cherry, and alder.
I hope this gives you some insight into the world of smoking foods.
Seeeeeeya; Goodweed of the North
