18-70mm: focal length of lens. 50mm is 'normal', anything less is a wide angle, any more a zoom (this changes when using most digital slr's, too much to explain here)
f3.5-4.5: f-stop, max aperture or 'speed' of the lens. the widest it can open. commonly referred to as speed since the wider a lens can open, the more light it lets in, the faster shutter speed you can use. lenses with wide apertures are termed, 'fast lenses', remember that f-stop is an inverse measurement, so f1.4>f2.8>f3.5.
g, ed-if, af-s: proprietary nomenclature from the manufacturer, in this case nikon, refering to the quality, features and purpose of the lens.
before you look at buying a dslr, might want to do some research on photo basics. not trying to be patronizing, but the more you know, the better chance you will get what you want and not pay for features you dont. it will also help you use and enjoy your camera much more once you own it.
fell free to ask more questions should they come up though, there are lots of photogs on ATOT
edit: touche' GTaudiophile, beaten to the punch. nice use of 'nomenclature' btw