Unlike the piano, the guitar has the same notes on different strings. Consequently, guitar players often double notes in chord, so increasing the volume of sound. Doubled notes also changes the chordal timbre: Having different "string widths, tensions and tunings, the doubled notes reinforce each other, like the doubled strings of a twelve-string guitar add chorusing and depth". Notes can be doubled at identical pitches or in different octaves. For triadic chords, doubling the third interval, which is either a major third or a minor third, clarifies whether the chord is major or minor.
Unlike many string instruments which use a bow to create a sound, guitars are played by plucking or strumming the strings on the instrument, which vibrate to create a sound. Chords are played when the guitarist holds their fingers down on more than one individual string to change its length, which in turn changes the frequency of the vibration created - in other words, it creates a different note. Performers often use guitar tabs, rather than sheet music, when learning music: this acts as a kind of 'map' to teach guitarists where to put their fingers on the strings.