I do this every single week at least once. I make a HUGE pot of beans and then I am good to go for quick beans and rice burritos all week for meals.
Take your beans(i usually use pinto but I do black, and various other kinds as well) and wash them thoroughly. Put them in the cooker and cover with water. I never measure, but I put a minimum of 3-4 cups of beans or more and then I cover with more than enough water. Lock on the lid and place on the stove on high heat. When your pressure cooker starts to blow steam time for 18 minutes. Then remove from the heat and let the steam finish and the pot cool down until the lock releases and you can open the cooker. Your beans should be ready to eat. They keep about 5-6 days as long as you cool them off quickly and keep them cold.
I wait and salt them as soon as I open the canner instead of salting before cooking. The whole think here at about at altitude of 5000ft. takes a little over an hour from beginning until ready to eat.