Playing a 24-hole harmonica involves the same principles as playing any harmonica. The standard harmonica consists of one row of holes, with each hole containing a single reed. A harmonica reed is a thin metal tab that vibrates and produces sound when air is blown into the instrument. Twenty-four–hole harmonicas have a top and bottom row, each row with 12 double-reed holes. When you blow into a hole, both reeds vibrate, adding a more full-bodied sound than single-row harmonicas.
Hold the harmonica in one hand with your thumb across the bottom and index finger across the top and back of the instrument, allowing room to place your mouth and lips fully over the holes. The numbers stamped above the holes must be facing upward.
Form your lips in a loose "O" shape. Choose any hole on the harmonica and place it against your lips. Moisten your mouth and lips to help form an airtight seal with the instrument.
Blow (exhale) into one hole to play a single note. If more than one note sounds, adjust your lips. Practice until you are able to play the single note with consistency.
Draw (inhale) into the harmonica on the same hole to play the second note, adjusting your lips if necessary. Practice blowing and drawing on the hole until you can play the two notes without adjusting your lips.
Move the harmonica across your mouth to the right, until the first hole (the lowest note) is against your lips. Blow and draw into the first hole. Proceed to the second through the 12th hole to play the entire scale. Play slowly, adjusting your lips as necessary. The goal is to play the two notes on each hole clearly.