The harmonica is a small, versatile instrument played in nearly every
kind of music and most cultures the world over. The harmonica, also
French harp, and mouth organ, is a free reed wind instrument used
worldwide in many musical genres, notably in blues, American folk
music, classical music, jazz, country, and rock and roll.
There are many types of harmonica, including diatonic, chromatic, tremolo, octave, orchestral, and bass versions. A harmonica is played by using the mouth (lips and tongue) to direct air into and out of one or more holes along a mouthpiece. Behind the holes are chambers containing at least one reed.
Though it may seem confusing to learn at first glance, the harmonica is actually an easy and fun instrument to get started playing. One needs to keep practicing playing scales and individual notes until they are comfortable with playing just one note at a time. Once you can exert that level of control over your instrument, pick out some simple songs and practice them as well.
Tablatures for songs like ?Mary Had a Little Lamb? and ?Oh, Susannah?. Although you can certainly continue to teach yourself, you'll see faster and more technically sound results if you practice under the tutelage of an experienced player.