To put it simply, baking is fully cooking food in an oven. Just about anything can be baked, including breads, desserts, fish, poultry, meat and vegetables.
The key in baking really comes down to the proper ratio between the oven temperature and the baking time, which can be determined by the size or weight of the dish. In brief, the larger and more dense the item, the longer it will take to cook, and the smaller and less dense, the less time. Something dense like a cheesecake, for example, will bake a high temperature initially for a short amount of time and then bake slowly at a low temperature to ensure even cooking throughout. A fillet of fish, however, cooks very quickly and is baked at medium-heat for a short duration.
Poaching is an incredibly versatile cooking method; just about everything from fruits to meats can be cooked using this technique. Poaching is merely simmering food in liquid until it is cooked through.
As with baking, the density of the food will determine the cooking duration time; fish is cooked for a short amount of time in liquid that is gradually heated, while denser meats cook longer starting with a cold liquid. The key to poaching meats and proteins is to make sure that your stove temperature is not too high, as this will cause the meat to break down, resulting in a greasy meal. Because eggs cook quickly, the liquid is first brought to a boil then turned off. Then, the eggs are added and covered until cooked to the desired doneness.
Sautéing is a method of cooking that requires that you use an appropriate amount of oil and a pan that allows for even cooking, while heating your pan to the correct temperature. If you cook foods at too low of a temperature, the water that is released will not evaporate and your food will not brown properly. Ideally, the water released from the food should evaporate on contact with the pan, which will allow for proper browning and produce the best texture and flavor.
Sautéing does not require a large amount of oil. Adding too much oil to the pan is a common mistake that many cooks make; this will result in either a crispy or soggy meal, depending on the temperature of your pan.
Steaming generally refers to cooking food set over (but not touching) boiling water and placing a lid or cover over the food. This allows the heat and moisture to remain within the pot while cooking. If done properly, this is a wonderful cooking method for cruciferous vegetables such as broccoli, cauliflower and brussel sprouts, as it allows for lighter cooking without leaching out a large amount of nutrients. It is often the case that harsher cooking methods for these vegetables will turn them a grey color, but steaming keeps their vibrant green color in tact.
While a pot with a fitted steam basket is ideal for steaming, you can also use a collander or strainer, provided it fits in the pot, with a lid.