To cook lobster at home, fill a large pot 3/4 of the way with water and a piece of dried seaweed, bring the water to a boil, kill the lobster and place it in the pot. Cover the pot, allow it to return to a boil and wait 20 minutes.
To kill the lobster humanely, place it in the freezer one hour before cooking it. Another humane way to kill the lobster is to quickly stab it between the eyes with a sharp kitchen knife. Some people say that lobsters should be boiled alive, as stabbing it first may ruin the lobster's roe, and can also cause protein coagulation to form in the water.
You can either fill your pot with fresh seawater if it is available, or add enough salt to standard tap water to make it taste like water from the ocean. When the water with a piece of dried seaweed in it has reached a rolling boil, place the lobster in, put the lid on top of the pot and allow the water to return to a boil.
At this point, a lobster that weighs between 1 and 1 1/2 pounds should take 15 minutes to fully cook, so add a few extra minutes for larger lobsters. It is better to cook a lobster too long than to undercook it.