Dietary Aide Interview?

You don't need to be experienced with food to be able to do light food prep. They're probably talking about fairly easy things you can already do like making sandwiches and chopping up some vegetables. If they ask if you have had any experience working with food, be honest and tell them that you haven't had any professional experience, but that you do cook at home and you cook for X number of people so you feel confident you can learn to cook for a larger crowd.