A note is an individual sign used in music that represents a specific pitch and a specific duration. Notes are conveyed on a musical staff and are designated by the letters A through G denoting the pitch. The duration is conveyed by the shape on the staff and is either a whole note, half note, quarter note, eighth note or sixteenth note. The duration is a fraction of the meter, or the timing, of the overall song.
A chord is a set of two to three notes played at the same time. A chord is used to harmonize a melody, build complexity and richness and define the key for the song. The most common type of chord is called a major triad, where a note, its major third and its perfect fifth are played together. A major third is the note that lies four half steps from the base note and a perfect fifth is the note that lies seven half steps from the base note.
Instruments are divided into two basic categories: monophonic and polyphonic. Monophonic instruments such as the violin, flute or saxophone can only play one note at a time. Polyphonic instruments, like a piano, guitar or banjo, can play several notes at a time to create chords.
Any notes can be played together to create a sound, but when chords are played correctly they create a sound in harmony. Appropriately used, the chords create a nice harmonic structure, which is best defined as the background mood of the music. From the initial cords, the progression of the sound can occur in a pleasing and methodical manner.