Generally speaking, products labeled for curly hair are gentle (because curly hair is often delicate) and designed to help reduce frizz and help with definition.

So it won’t make straight hair curly, no. It will help curly hair look “curlier” because less frizz and better separation of the curls makes it look curlier, but it doesn’t literally tighten them, may even relax them very slightly.

So they are for people with curly hair, to improve the look and/or health of curly hair.