Use the adjective informative to describe something that gives you some kind of useful information, like an informative book about identifying the mushrooms you find growing wild in the woods near your house.
When something is informative, it's usually educational and full of facts — like an informative text book or an informative tour of the Hindu temples of northern India. If you learn a lot from something, you can call it informative. The Latin root of informative is the word informare, which means "to shape, train, instruct, or educate." Something that does those things for you is informative.