What shoes should I wear to the Martial Arts Class?

Hello Guys, recently i have joined a Martial Arts Classes to learn the techniques and to get the training.I have also order a shoes pair from "WKC Martial Arts Supplies". But yesterday one of my friend told me as Occasionally the class will meet outsidesome so it will be conducted on barefooted and for other sessions it will be on wearing shoes.So i want to know in which cases i can wear the shoes. Waiting for your valuable suggestion.