Soak the acorns for a few hours. If the water was safe to drink, taste a piece of acorn to see if it is still bitter. If you don't like it, dump off the water (which should be brown like tea), add fresh warm water and soak the acorn pieces again for a few hours. Repeat this a time or two, or three depending on the acorn's bitterness. Once they taste "OK" (read here: bland), let them dry out for a few hours. Then you can run them through a grain grinder, flour mill, or the classic mortar and pestle to make acorn flour. Add this flour to existing recipes; or try your hand at making acorn porridge or hard, brown biscuits.
How do you tell if you picked the right nuts and berries to eat?