I USE 2 PAIR OF READING GLASSES 3 POWER AND 2.75 POWER
If you can't see it you can't do it
Get you a stave that is not any good, or one that has plenty of thickness and get out side in the light.
sand 1 end and sides for about 12" or so you can see the ring running down the sides and end.
*****look at the end and sides you can see the two different colors***** early and late growth rings
Take it slow, the best way to learn is to DO IT. when you get to a different color (lighter) of wood, keep moving down the stave, come back with a cabinet scraper and scrape on that different color wood until you see your ring.
EARLY GROWTH RINGS ARE THINNER AND SOFTER, LATE GROWTH RINGS ARE THICKER AND HARDER
If I missed something guy's please add to or correct me.
I like this youtube by Clay Hayes
Building a Selfbow - Part 1: Backing an Osage Stave