A diatonic harmonica's simplicity makes it a great choice for the beginner. Most harmonica teachers recommend starting out with a 10-hole diatonic harmonica tuned to the key of C. The Hohner 1896 Marine Band 10-hole diatonic harmonica in the key of C makes a great beginner's instrument.

With regular deliberate practice, you can expect to be playing simple pop tunes within around 3 months. Within 6 to 12 months, your technique will improve and you will probably be able to work on bending notes (a very important skill for getting the best out of a harmonica).

There is no difference. A harmonica is a mouth organ. There is another instrument called a glass harmonica that is not a mouth organ, but a musical instrument consisting of a series of rotating glass bowls of differing sizes played by touching the dampened edges with a finger.