A better view of the finger action is in the following clip:
Note that this was filmed during prunning season and the my hands are beat up from being out in the orchard.
This basic technique can be used for anything from socks, mittens, hats, and baby clothes to ganseys, rugs, and circus tents. It can be used for knitting in the round or back and forth. You can use more needles to knit larger items. This technique is appropriate for fine lace. and, I like a knitting sheath better than a knitting pouch/belt for Fair Isle.