A couple of videos describing the workings of a brushless motor by Texas Instruments:
Brushless DC Motors & Control - How it Works (Part 1 of 2) - YouTube
Brushless DC Motors & Control - How it Works (Part 2 of 2) - YouTube
Brushless DC Motors & Control - How it Works (Part 1 of 2) - YouTube
Brushless DC Motors & Control - How it Works (Part 2 of 2) - YouTube