Clad means "dressed or covered." Most kids go to school clad in jeans and t-shirts, but students in the Shakespeare club might show up clad in velvet gowns or leather breeches.
As it applies to what a person is wearing, clad is the past participle of clothe. If you wanted to talk about the day your friend commanded you to clothe yourself in green and you obeyed, you'd say, "I clad myself in green." Of course, it sounds archaic. Like talking about your shoes by saying shod.