Become a fan of h2g2
The harmonica has the glorious distinction of being, perhaps, the most respected, most incredibly portable instrument in history. The length of an average person's index finger, this ten hole wind instrument packs quite a wallop of volume, and, to the skilled player, it can actually produce some incredibly beautiful sounds. You haven't lived until you've heard 'Amazing Grace' belted out by a pro on one of these things. Or at the very least, 'Camptown Races'.
Originally used by slaves as a means for their own creative expression, the harmonica has been a blues staple since its birth. Rockers such as Bob Dylan, Neil Young, and The Beatles helped introduce it to other audiences. It's also a surprisingly complicated instrument to learn. Its deceivingly simple appearance makes it seem as if just anyone can pick it up and blow out a tune. Little do most know that it takes a solid four hours of practise before that can happen.
Actually, the only reason it's easier for most people to learn is that it's so convenient it can be played and practised no matter what the person is doing. On their lunch break, while commuting, surfing the web, or even making love1.
If you'd like to learn how to play the harmonica, buy one. Listen to lots of Bob Dylan. Drink some root beer2, too.
Pick it up and stick it deep in your mouth.3. Blow on the five, suck on the four. Blow on the five, suck on the four. Doo-dah. Doo-dah.
If you wish to learn anything more advanced in the way of 'harping', just experiment on your own. It's a fine little instrument to learn by yourself, and before you know it you'll be raking in coins in the subway just like a professional vagrant.