What lenses are compatible with the Nikon D3100? - 1

Basically my main question is when searching online for a lens how do i know if one i like is compatible with my cam. What do i have to look for?

For example in the link below i saw this lens which is at a pretty good price but i noticed the format is FX and my other lenses are DX format… Is that an issue?

http://www.nikonusa.com/...-5.6G.html

And yes i'm a rookie at all of this… Hence the rookie level camera…

Click the link for more information

http://www.kenrockwell.com/.../d3100.htm

Nikon cameras, whether they are DX or FX, can use any DX or FX lenses, except, If you have an entry level camera like the D3000 or D5000 series cameras, you need to buy AF-S lenses (DX or FX) if you want to be able to use the camera in the auto-focus mode

Nikon lenses that give full functionality with your camera are called AF-S.

That particular lens won't autofocus with your camera - the manual explains why.