question about DIFFERENTIALS !!!

HI

I want someone to explain to me * differentials *.
How do the numbers work like the gear ration 3.73:1 or 3.93:1 or any other combination.
What do the numbers mean?
What's the difference between LSD and the other types of differentials?
What differential is better for top speed/ wich one is better for quick starts???

Someone please educate me .

well all i know is you sacrafice top speed for quick starts, and lsd is both wheels spin, instead of one. w/ a high output engine you can afford to have a lower gear ratios.