Because the beans expand while cooking, periodically adding small amounts of water to the pot will keep them adequately covered, ensuring even cooking. Properly soaked beans usually require between 30 minutes and 2 hours of cooking. Cooking times will vary depending on the variety of dried bean.  Black beans: 60 minutes Light/dark red kidney beans: 90 to 120 minutes Navy beans: 90 to 120 minutes Great northern beans: 45 to 60 minutes Pinto beans: 90 to 120 minutes Ideally, your beans will be tender but not mushy. If your beans are still crunchy or underdone after the recommended cooking time, continue cooking at a simmer, checking every 10 minutes for doneness.

TL;DR in Chinese:
把豆子放在一个大锅里，加足够的水，要能完全盖住豆子。 在锅里加一勺子植物油或者橄榄油，这样就不会有太多泡泡，煮得到处都是。 小火或中火煲豆子。 选择正确的烹饪时间。 你可以用叉子或者两个指头来试试看豆子是否煮好了。