Some information from Wikipedia:
The mountain dulcimer is a fretted string instrument of the zither family, typically with three or four strings. It is native to the Appalachian region of the United States. The body extends the length of the fingerboard, and its fretting is generally diatonic.
The traditional way to play the instrument is to lay it flat on the lap and pluck or strum the strings with the right hand, while fretting with the other. The dulcimer may also be placed in a similar position on a piece of furniture, such as a table or chest of drawers, to enhance the sound. There are two predominant methods of fretting. First, the strings may be depressed with the fingertips of the fretting hand. Using this technique, all the strings may be fretted, allowing the player to produce chords. Second, the melody string, the string closest to the player, may be depressed with a "noter," typically a short length of dowel or bamboo. Using this method, only the melody string is fretted and the other strings act as drone strings (the melody string may be doubled, so that the melody can be better heard over the drones). In this second style of playing, the combination of the drone strings and the buzz of the noter on the melody strings produces a unique sound.
Example of playing:
