In your Dolphin DashBoard, click on Content and select Classifieds. This is were you manage or construct Cats and SubCats. To Add a Cat select Add and type the name and description. To add SubCats to a Cat you need to select the Cat in the Drop Down which will activate the SubCat controls which are all below the Cat Field.

Remember everytime you create a new SubCat "MAKE SURE" you are in the proper Cat. Just adding SubCats puts them in the default Cat.

Hopes this helps