In the past year or so I realized that I use layer masks in Photoshop a lot. I thought I'd do a video tutorial on how and why I use it since for years I had no clue what it was and avoided using it.
I hope it's helpful!
P.S. After looking at the video I realized that I should have said this approach of separating out a character from the background is for those people who paint using transparent brushes like I do. If you painted with flat opaque colors, then you can just move your layer around with no extra special preparation.
In my case, I paint using very transparent brushes. If I didn't use the mask with the white background, then the background will just show through the entire character.