When you disrobe, you take your clothes off. Before you go swimming, you should probably disrobe and put on a bathing suit.
Everyone disrobes, before we take a shower, change our clothes, or go skinny dipping. To disrobe is simply to get undressed. You might disrobe in a dressing room to try on a tuxedo or disrobe before your karate class so you can put on your white karate gi. The word uses the prefix dis-, "do the opposite of," before robe, with its old fashioned verb sense of "clothe."