The tutorial is meant for mods created with the modkit wizard. When creating something with the modkit wizard just chose the category you want to create your mod in, then just follow the same tutorial.
However, mods created through the wizards currently create a bug where blonde hairs become brown and other hairs gain a grey undertone when you have those mods in game. There is a way of making tops and bottoms as mods without the wizard, and I have a tutorial here if you want to check it.