Nikon d3000 cap storage?

So we got a Nikon d3000 last year, and I love it! It comes with two lenses; one that zooms in and one for normal photo captures. Inside the camera case is a string-drawn bag to hold one of the lenses in and at the bottom I found something that I think attaches to the camera… It looks like it could attach to the outside of the lens to create shadows or a more direct shot? Or i don't know if its just for storage? Anyways what is it for? Its al black and is round but gets to a bigger circumference the more outward it goes?

What does the user manual say that came with your camera?

Lens hoods are designed to prevent lens flare when you have a light source that strikes the lens at an obtuse angle

That is called a lens hood

they are not really needed now-a-days, but they are used to stop some lens flare. You can put them on and use them as protection as well