To be honest this is a really simple feature to use but hard to explain to someone that has no idea what quantize is, but I'll try my best. Here is a brief explaination from wikipedia I doubt if this will shed much light but..
http://en.wikipedia.org/wiki/Quantization_%28music%29
Other than that I would say turn on any quantize amount(i.e. 1/32 notes) and then hold note repeat this will show you how quantize lays the notes down, change the quantize (i.e. 1/8 notes) and hear the difference. Then try making a beat with each quantize and listen to the difference. Basically quantize is like a grid of notes you are allowing yourself to use in each bar, 1/8 notes you'll only be able to put down a maxium of 8 notes per bar, 1/16 will be a maxium of 16 notes per bar and so on. Turning quantize off will allow 96 notes per bar....I think.

....anyway I hope this helps.
