This tutorial video explains what quantization is, and how to quantize in FL studio - or Fruity Loops to give it its full name.
The FL Studio Quantizer is used to automatically make adjustments to the start time and duration of notes that you have played into a piano roll from a midi keyboard. Alternatively it can be used on static scores that you have created using the pencil tool.
There are three versions of the Quantize tool: Quick Quantize, Quick Quantize Start Times, and The Quantizer. This tutorial guides new users of FL studio in the techniques of using the this tool.