Preferably you want to get your crabs alive. Some say you should kill them before placing them into boiling water, as this is kinder to the crab: turn them over and there is a flap; lift this to reveal a slight dip then with something like a knitting needle and hammer, spear the crab, aiming towards the front of the crab and down. I am afraid I just drop the living crab into boiling water, which must be as salty as the sea otherwise water will leach into the crab, resulting in wet flesh. Cooking time depends on the crab’s size; as a rough guide, for the first pound allow 15 minutes, then another 5 minutes per further pound.