How to put my new lens on my nikon D3100?

I have a Nikon 50mm f/1.8D AF Nikkor lens and a Nikon D3100
I match up the two white dots then i twist it to the left and it stops but the camera says that there's no lens attached.
i don't want to break it so i really need advice on how to put the lens on

Sounds like something isn't working correctly between the body and the the lens. You should feel it almost 'click' into place as you mount the lens.
You do realize that you will have no auto focus with that lens, correct? In order to have the AF work you must purchase AF-s lenses for your camera. Considering that something isn't working properly between the body and the lens and that you have the wrong lens for AF I'd be returning it and getting the correct lens. If you bought it locally take your camera in with you so you can make sure you are mounting correctly.

When it "stops", you need to go a little further and make it click into place. Have fun with this manual focus lens or trade it up to an AF-S lens.