if you just have them in a tank w/ no filters or plan to use them all w/in a few weeks, then don't feed them.
if you keep them in an aquarium w/ a filter, you can feed them fish flakes....like goldfish. they learn to eat them in a few days. don't feed them right away. also, need to clean the tank regularly. they can last a long time (months) if you take care of them.