The six words

nfty uses a cooking metaphor. Learning these six words is learning the app.

Word	What it means	Saved as
CookBook	Your whole project. Holds the canvas size, the collection's name, and its Recipes.	.cbk
Recipe	One type of character -- its full stack of layers, in order, plus its rules. A book can have several.	.rcp
Ingredient	One layer: "Background", "Eyes", "Aura". Holds that layer's kind, its coloring, and all its options.	.igt
Variant	One option inside a layer -- a single drawing, with a name and a weight.	(inside an Ingredient)
Set	The finished output: the images, their data, the rarity, and the seed that made them.	.set
Kitchen	Your shelf of loose parts -- Ingredients and Recipes that belong to no one CookBook.	.ktn

So: a CookBook holds Recipes, a Recipe holds Ingredients in order, an Ingredient holds Variants, and cooking the book produces a Set. A Kitchen is not part of that chain at all -- it is the shelf the chain draws from: loose parts that belong to no one book, ready to be pulled into any of them.

Why a metaphor at all

Because the alternative words are worse. "Project", "template", "layer", "asset" and "collection" are each used by three other tools to mean three other things, and the relationships between them would have to be memorised separately. The kitchen ones carry their own structure: nobody needs to be told that a recipe lives in a cookbook, or that ingredients are what a recipe is made of.

The one place it strains is Variant, which is not a cooking word. It is an option inside an Ingredient, and it never gets a file of its own.

They are all just zip files

Every one of these is really a .zip with a different extension. Rename one and open it with any unzip tool to see exactly what it holds. There is no hidden database and no proprietary blob -- see File formats.