I'll try to give you a quick explanation, because getting the back of your bow to one ring will be very helpful in its structural strength.
Think of it like this. If you have a log from a tree and split it into quarters, each quarter will have a cross section that looks similar to a piece of pie, with the bark being the crust. The bark side is going to be the back of your bow (the side that faces away from you when shooting). So if all you do is strip off the bark, the outer most ring of the tree will be covering the entire back of the bow. Meaning the back of the bow is at "one ring" (no LOTR jokes). Does that make sense?
Some woods can actually be done this way. Just strip off the bark, and you're done. But sometimes the outer ring might be damaged. Or the second or third ring (from the outside) might be a bit thicker, so you want to have that as the back. You need to (carefully) cut away the outer rings of the tree until the ring you want covers the entire back of the bow. This is usually done with a drawknife.
This video isn't too bad:
https://youtu.be/z8aRn9dXxE0