The following video chapters highlight the core functionality of PixInsight. They are shown in the suggested order of review. There are generally multiple sections within each chapter. 

If after FastTrack and QuickStart!  you *must* jump right into the step-by-step (without knowing the "why"), you can then go to the Fundamental Workflow sections and review examples such as NGC1333 and M42 as well as many others.  Really though... please do FastTrack and Quickstart first!.