what difference to the oher lenses make?
obviously macro ones are for macro etc
refine your question a bit better....
bigger leses (higher mm number) give you the ability to zoom in more, or take pictures of things further away.
the lower the number (mm) the wider the angle so you can stand closer to things and get more of the surroundings in.
50mm is the equiv of what you see out of your eyes.
the smaller the F number the faster the lens, so a 50mm f2.8 will shoot better in darker locations where as a 50mm f8 would need a tripod as you would have to lower the shutterspeed to get the same image...
alot of the more expensive lenses have image stabilization or vibration reduction which allow you to go a stop lower than normal without the use of a tripod.
macro lenses are for close high detail work.
telephoto is big lenses for far away work.
wideangle is for getting more stuff in at close range...
fisheye gives you the curved stretched distorted images you see in skateboard mags etc.
you get fixed lenses that are just one mm setting i.e the nikon 50mm it only does 50mm.
you can get mirror reflex lenses which allow a high fixed zoom but more compact however they are normally pretty slow (around f8)
basically lenses that are big zoom with a f number like f2.8 are expensive well most lenses around f2.8 are expensive....
oh and macro lenses have different enlargement ratio's so 1:1 will be normal and 2:1 would be double and so on...