What size lens for NIkon D3000?

I'm wanting to purchase a low light lens online, but i have a dumb question. Does a camera only take one certian mm size lens or could you get different size mm lens that will fit on the same camera?

Almost all Nikon lenses will fit your camera.

The least expensive low-light lens is the Nikon AF-S 35mm f/1.8. Other notable lenses are the Nikon AF-S 28mm f/1.8, the Nikon AF-S 500mm f/1.8, and the Nikon AF-S 50mm f/1.4.

And, check out the new Sigma 17-35mm f/1.8, which is a zoom lens. It is available in the NIkon mount (as well as Canon - so make sure you get the version designed for Nikon).It should be released by the end of this month.

The D3000 takes ANY lens in Nikon AF-S fit.

Nikon AF fit lenses will meter, but won't autofocus.

The older AI, AIS and Series E lenses fit, but allow neither metering nor autofocus, and your manual should explain this.

The mm is about the focal length of the lens which is more or less angle of view. You can use any number of mm for your camera as long as it will fit the camera. Here's a lengthy discussion about focal length.

http://keerok-photography.blogspot.com/2011/05/lenses-so-many-of-them-there-is-no-best.html

What's important is the mount of the lens. That is the part that goes in to the camera. The mount system must be the same that's why it is recommended to stick within the brand of your camera for lenses. Different camera brands are not compatible with each other when it comes to lens mounts. If you try to get a third-party lens brand, make sure you are getting a lens with the same mount as your camera.