I think you will be better of with searching the Community for AQL, as this question has been asked several times before.
In short, it is just an abbreviation for the script language used to write Qlik load scripts. For any details on how the load script is constructed;
- Study the QlikView reference manual or Qlik Sense Help
- Do free online training (QlikView Free Training - Business Intelligence (BI) Reporting Software Solutions | Qlik)
- Do class room training (http://www.qlik.com/au/services/training)
- Study demo apps to see how they are constructed (Qlik Demos: See QlikView in Action | Demo.Qlik.Com)