Lens hood for my Nikon D3100?

I just discovered I had a lens hood for my Nikon D3100
This might be a really dumb question but how does the hood go on the lens? I looked in the users manual and they mention nothing about a lens hood.
Does the hood fit tightly on the lens or loose?
Does it screw on tight?
I'm not sure
Also what use can I get out of using a lens hood?

in case anyone is wondering what it looks like its this:

If you look at the lens hood, you will see either threads or a bayonet mounting feature.

The hood prevents ghosting and lens flare if the is light shining toward the lens at an obtuse angle

Lens hood usually reduces flare.

it's also protects you from birds diving into your lens and bits and pieces flying everywhere during a mud fight. (well, maybe not a mud fight) If a guy gets mad and wants to punch your camera, he'd have to get through your lens hood first, or scrunch his hand really small to fit it in there to punch the glass. If by any chance you encounter a volcanic eruption, the magma would need to pass your lens hood before it touches your lens (assuming it's coming head first)

screw the lens on! You'll probably won't notice a big difference but it does help.
it screws on tight and is designed to stay on the lens for protection (physical and flare)
it makes you look SUPERPRO too.

Other uses for a lens hood:
-you can use it as a cup if you put your hands underneath it while drinking.
-you can use it as a bowl for ramen if you use it as a cup
-you can melt the plastic and sell it for parts
-you can grow a plant inside it.
-you can make a little hamster wheel that goes in circles for your adorable hamster
-you can put it on your mouth and amplify your voice (not really, but yeah… )
-you can put it on your head like a hat
-you can give it to your cat
-you can look through it and pretend it's a monocular

oh the joys of a lens hood.

It matters what lens you have

the kit 18-55mm uses a clip on lens hood, basically there are two tabs that you press in, and just stick it on the end of the lens

other lenses have a screw on lens hood. Match the dots up and twist right (righty tighty, lefty loosey)

It should be the small circular hood for the 18~55mm kit lens. Just push it in from the front of the lens. To remove, press the two tabs at the rim (hood) then bull it back.