Music is an art form that incorporates sound and silence to form melodies and harmonies. Musicians base their sound on rhythm.
A melody is a series of notes that listeners here in the song. For example, in a pop song, the lyrics that the singer is singing is the melody of the song. For the most part, instruments/singers with higher ranges get the melody of the song. Sopranos (girls) sing higher notes, so they often sing melodies in songs, especially in choirs. In an orchestra, violins and violas play the melodies. When playing the piano, the right hand plays higher notes, so it plays the melody of the song. For more information about melodies, visit the Wikipedia site.
A harmony is a backup series of notes that accompanies the melody to enhance the sound. Harmonies are not always heard because they are lower than the melodies, but they do make the sound of the song richer. In a choir, the altos (girls) and baritones (boys) sing lower notes, so they harmonize with the sopranos. In an orchestra, cellos and basses play harmonies. On a piano, the left hand plays lower notes to harmonize with the right hand. Often times, the left hand will play chords, which also works to harmonize. For more information about harmonies, visit the Wikipedia site.
Rhythm is a measure of beats that go in a cycle throughout a song. Drums give the rhythm in songs. If there are no drums involved, the conductor (especially with choirs) gives the rhythm. For more information about rhythm, visit the Wikipedia site.