The arrangement of the tuning pegs on a Tinkers Damn dulcimer may initially be a little confusing. I hope this diagram will help clear things up. It shows the head of a right-hand dulcimer in a tuning of G-C-G-G. There are other possible tunings for a dulcimer but the one shown here is a good place to start. The small letter on each string is the note played by that open string, and the arrows point to the knob used to tune the named string. If you use an electronic tuner you can adjust the strings in order by working around the tuning knobs in a counter-clockwise direction starting with the knob farthest from the top of the instrument.
The standard way to play the instrument is to fret only the two G strings on the right side of the image above, while the other two strings are drones, they always play G and C. It is possible to fret more than just the two G strings to form chords, but for the simplest no-fuss strumming you’ll find that pressing just those two G strings to any fret will make a pleasant sound. That’s the magic of the diatonic scale of the dulcimer frets. It limits the chords that are possible but makes the instrument a delight to casually play on its own.