I can play simple songs on the harmonica. We have several. Hmmm, I don't see alot of folks playing celtic music on them but I guess you could. Do they make music books for that?

Spare us the "celtic" schlock, but yes Scottish music like marches, strathspeys, jigs, reels and slow airs work very well on harmonicas. I play every week with a guy who's been doing that for 50 years.

There are no good books I know of, but check out Sam Hinton's YouTube videos (mostly American music but the techniques are exactly what you want for Scottish too).

first of 17 Sam Hinton videos