POTATOES - HOW TO CHOOSE AND BOIL THEM
Potatoes differ in starch and water content - the more water the less starch, and vice-versa. The new potatoes have a lot of water and are more sweet and provide a sense of freshness with some 'flowery' notes. New potatoes are usually not peeled, since their skin is so thin and tender, especially when cooked, and it also gives some extra flavor to the cooked potato. New potatoes taste best if they are cooked simply: boiling or roasting does simple magic to them.
Another type of potatoes is more starchy and less watery, and these are the type you want to use in purées and for baking. They are also good for deep fried chips since the high starch content makes them more tender, and the low amount of water minimizes the sputtering once the potato is thrown into the hot oil. Because of the high starch content they also make a good liquid-absorbing sort of potatoes, which is what you want when baking them in milk and cream, as is done en casserole. A number of starchy potatoes exist, Idaho is a famous sort, and russet is another one. These last mentioned potatoes are good for baking with their skin on.
The all purpose potatoes are the ones that are somewhat in-between high and low starch, with moderate water content. These include chef's potatoes, Maine, and also the red skinned and waxy yellow potatoes that have a very good and popular flavor. The fine thing about them is that they don't fall apart even if they are cooked through, so they can be used in many dishes where you want to present the potatoes in some special shape. Since they are all purpose, you can use them in boiling or sautéing, or even for roasting.
Cooking potatoes is usually done by boiling them. Steaming can also be used, although it is not a common technique (you don't use fat in boiling anyway so no need to substitute). To boil the potatoes, you first need to choose the type for your dish - do you want purée (choose starchy potatoes) or do you want to have a fine shape and flavor (choose waxy potatoes). Then, you should decide if you want to cook them through, or to parcook them for use in e.g. sautéing. The choice is yours.
To prepare potatoes for boiling, rinse the skin with water and scrub them if necessary. Peel them before boiling, or after boiling (they have some finer flavor in my opinion). Make sure though to always remove any green parts of potatoes, which contain a toxic substance called solanine. Also remove any dark eyes and other grotesque-looking parts. Once you've peeled the potatoes, put them directly into cold water, otherwise they will start to oxidize and lose their color. Now, put the potatoes in cold water into a pot and put it onto a hot stove. The reason to start cooking them in cold water is to ensure an even cooking - throwing the potato into a boiling water will quickly soften their exterior before the interior gets cooked. To the boiling water, add some salt to give the potatoes some extra flavor. Cook the potatoes in simmering water for best flavor and even cooking. It will take a while but the potatoes will taste wonderful. Cook them until you can stick a fork into the potato and it can be easily removed, but no longer than that! Potatoes should not be overcooked and fall apart. They should be tender, soft and hold their shape (unless they are very starchy). Then drain the water from the potatoes, and put the pot back on low heat to evaporate the rest of the water, until the steam disappears. Make sure to shake the pot from time to time to not make potatoes stick to the pot. That's how to boil potatoes.