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Dried kidney beans need to be soaked in water before being boiled and cooked. For the best results, soak beans in a pot full of cool water overnight at room temperature.  It's a good idea to sort through the beans before hand and rinse them off, to remove any dust, sediment, or tiny pebbles that might have gotten mixed in. Rinsing them in a colander is usually fine. Without soaking and cooking thoroughly, kidney beans contain phytohaemagglutinin, also known as kidney bean lectin, which causes gastric distress. To avoid this, they need to be cooked at least 30 minutes, at boiling. If you don't have the time to soak beans overnight, you can also do the speed-up method. Bring dry beans to a boil, then turn off the heat and let them soak for about 2-3 hours. Discard the soaking water and cook normally. Beans are probably most commonly cooked by boiling them in a pot of clean water, on the stove top, for a few hours. There are a variety of ways to cook beans, however, depending on what you have available.  Another traditional and speedy method is cooking kidney beans in a pressure cooker. Soak the beans normally and lock the lid in place, then follow the instructions for your particular pressure cooker. Canned kidney beans do not need to be cooked. You can add them into any recipe that calls for beans without cooking them. After soaking the beans, rinse them thoroughly in fresh water and cover the beans with enough clean water to cover them by approximately 2-3 inches. Then, cover the pot and bring the water up to a boil, immediately lowering the temperature and uncovering the pot when the water starts to boil. Cook beans at a very gentle simmer. You want a pot of beans to barely be moving, so they'll cook evenly and as thoroughly as possible.  Cook the pot with the lid on, but slightly ajar, if you want a creamy pot of beans, and cook uncovered for firmer beans. Check the beans after 45 minutes, pulling a few out and squeezing them between your fingers, or try to chew one. After a while, they should be soft and creamy. When they've reached the desired consistency, remove them from the heat. Stir the beans periodically to turn them over, ensuring that they'll cook evenly and thoroughly, and make sure the level of the water stays above the level of the beans as much as possible. Beans cooked a rolling boil will cook, but they'll split very quickly and become mushier and mealier than beans cooked more slowly and more gently. If you want, you can continue cooking beans for as long as you want, to get the texture you're looking for. Mushy beans are great for dips, curries, and lots of other dishes. As kidney beans cook, you'll notice a grayish-reddish foam start to appear on the top of the pot. That's the lectin cooking off, and the best thing to do with it is periodically skim it off with a spoon and discard it by rinsing it down the drain. It's very important to cook dried beans unsalted, or the beans will take much longer to cook, and might not actually cook at all. While some varieties of beans will take longer than others, some varieties (like garbanzo beans) will never get fully cooked if they're cooked in salted water.  At any point in the cooking process, you can add chopped aromatic vegetables. If your recipe eventually calls for onion, garlic, carrots, or other vegetables, you can add them to soften them up at any time. If you'd like the vegetables firmer, add them later in the cooking process. Softer, add them earlier. It's also common to add a ham hock or a pork bone of some type to a pot of beans, for added flavor. This is especially common for rice and beans, described in the next section. Beans are somewhat variable in their cooking time. It's usually common to have to add a little bit of water while the beans simmer away, to keep them cooking evenly. This may result in there being some water left over when the beans are done.  The general rule of thumb is to add three cups of water for every cup of dry beans you add to the pot. This should theoretically end with a pot of cooked beans and no water. It's also common to save most of the liquid in the pot, which can make for a nice gravy. Depending on what you're making with the beans, you won't always have to strain it.

Summary:
Soak dried kidney beans in cold water for 8-12 hours. Choose a cooking method. Simmer beans gently for 1-2 hours. Skim the foam off the top of the pot, periodically. Add salt and season when the beans are nearly soft. Strain the water off the cooked beans, if necessary.