All you have to do is use the row counter like you'd use any stitch marker, and put the first ring onto your needle. As you work your way back around to the row counter, you move it up to the second ring. You can keep moving the row counter up the rings each time, up to 10 rows. The counter also comes with an opening stitch marker, so you can move that up the rings every 10 rows, and count all the way to 100!
This tool can be used in-the-round or flat, and is especially useful for when you're working on sleeve decreases, raglan increases, hat decreases, and sophie scarves!