When young they should eat every day as much as they want once a Day. Leopards aren't like other lizards in the sense they know when thier full and really won't over eat. When they get older they will eat every other or every two days. Honestly i don't really keep track of how much mine eat now. But, they always have food in thier bowl so I don't worry about it. You are asking a lot of pretty basic questions. Have you read any care sheets on leopard geckos? If you haven't I suggest you hit google up and do some research.
Good luck with your leos they are great pets and have a ton of personality. They gave the oddest facial expressions to.