Every mouth bow begins as a flexible wooden slat or stick. If the center of your slat can be flexed 2 inches off the straight, it's sufficiently resilient.
Photo by Rick Sell
A wooden tuning peg from a violin adjusts the bow's tension. Here we see the tuning peg, holding peg (optional), screw, and string.
Set the tension.
Lay the bow against the hollow of your cheek and make music!