Hides are a fundamental resource in Ark and are used in a wide variety of crafting projects. Hides are also used in the creation of Gasoline, which is the principal fuel source in Ark.
Hides are harvested from the various creatures found in Ark. For the most part, the bigger the creature, the greater number of hides you may get from it. The best tool to use for harvesting hides is the hatchet, with metal being far better than stone. While smaller creatures may only yield one or two hides, the larger creatures can produce much more. This is a random drop, however, and it is entirely possible that you won't get any hides from a smaller creature.