How to make an old chair back into a bathroom towel holder?

Here is the DIY for one I made https://www.homeroad.net/2016/02/repurposed-ladder-back-chair-shelf.html

Here is a towel rack made from a beach chair but the back of any chair would probably make a rack. I hope this helps. If you need more ideas type "chair back to towel rack" and hit enter in the search box and you may find one you like better. I chose this one for you: https://www.hometalk.com/diy/bathroom/organizers/vintage-beach-chair-to-vintage-beach-inspired-towel-rack-1315597

Vintage Beach Chair to Vintage Beach-Inspired Towel Rack

"Using seat as stool" ?? just hang your towels from the back and sit on seat part-cut off legs if you want it more like stool but your towels will drag on floor.

I like this particular version as you get a little shelf as well as a towel rail, enjoy your making :) https://www.bhg.com/decorating/storage/projects/how-to-make-a-ladder-back-shelf/