The wok is one of the most adaptable, versatile cooking vessels ever invented. While originally intended for preparing Chinese food, it can and does take the place of multiple cooking utensils for all types of cuisine. It is marvelous for stir-frying (its original purpose) but substitutes very nicely for a saute pan, a standard frying pan, a deep fryer, a stock pot for soups or stews and a smoker. The shape of the traditional wok -- high, sloping sidewalls and a bottom that comes to a rounded point -- lends itself to many different uses. When used on a gas stove in conjunction with a wok ring, the ability to use different levels of heat simultaneously in the same vessel opens up all manner of cooking possibilities.
A wok was originally used for meat and vegetarian stir-fry dishes. As the oil used in the wok continuously drains toward the center of the bottom, the amount of oil necessary for stir-frying is much less than in a standard saute or frying pan. The high, sloping sidewalls make it very easy for the cook to turn and stir the contents of the pan continuously. This allows for more control over the relative doneness of the items being prepared. When the item is nearly done cooking, the cook can move it over to the cooler sidewalls. This allows it to continue cooking a bit longer at a much lower temperature without burning; this also makes room in the center of the wok for other items that need to be cooked at high temperatures.
Other wok cooking methods
Using the wok as a deep fryer is merely an issue of adding more oil to the wok. Preheating a wok prior to adding any amount of oil is the preferred method. When deep frying, remember that the center of the wok is considerably hotter than the periphery, so the item being deep-fried needs to be turned and rotated from center outward on a continual basis. Keep this same idea in mind when using the wok for boiling or as a stock pot. As with any deep, large pot, using a lower level of flame and allowing for longer cooking time is more effective than attempting to "flash boil."