Many dulcimer players learn songs by ear and others learn with Tab. Tab is a form of musical notation. Most dulcimer players learn songs by a combination of learning the tune by ear and by referring to the Tab ...
Tab is available from a number of sources, some free some you need to pay for. Please note that, in general, the tab you pay for is far better, both in quality and accuracy, than any of the the free tab you can find.
Other Free Sources:
Not so free ... but absolutely fantastic :
Larry Conger (Individual songs on Sheet Music Plus)
(If I am missing someone's awesome books ... please contact me!)