I found a great Youtube channel for learning how to arm knit. Simply Maggie has several videos from beginner arm knitting to specific techniques and methods. The audio can be a bit off, but overall, the quality of the explanation is pretty good. Below are some of the videos and a link to the Youtube channel.
Arm Knitting 101
3o Minute Scarf
45 Minute Blanket
There are also some videos for specific stitch types for those who want to take on more complicated projects.