AF-S = Auto focus lens driven by a Silent Wave Motor in the lens.
18-70mm = Focal range.
f/3.8-4.5 = widest aperture for shortest focal length/longest focal length.
G = Lens has no perture ring on it. Aperture to be set on camera body.
IF = Internal focus.
ED = Extra-low Dispersion glass is used on that lens for better image quality.
For Nikkor lenses you can read up on these two sites.