Difference between Nikon Nikkor AF 50mm f/1.8 D and GLens?

Thinking of buying Nikon Nikkor AF 50mm f/1.8 Lens. What is the difference between G or D that is stated on the les?

is G the newer version of the lens?
Will both lenses autofocus on my Nikon d3100?
Does the letter matter for something important

The G is newer than the D, and has a built-in AF motor, while the D has screw-driven AF. You will need to buy the G version if you want AF on any lower-end body (D40, D60, D3x00, D5x00). The G version is also better optically.

The "D" marking indicates that the lens can transmit focus distance info to the camera body, which helps with calculating flash exposure. The "G" marking indicates that the lens has no aperture ring, and is unusable on certain older film bodies. "G" lenses transmit focus information as well.