The guitar produces sound when it strummed (fingers run across the strings) or plucked. The guitar evolved from the lyre and medieval instruments known as the cittern and gittern. The resonating chamger of the typical guitar has a flat or slightly rounded back, a shape that resembles an "8," and a hole through which sound is projected. Along its neck, which holds six strings, are frets which guide finger placement. Keys are used to adjust the steel or gut strings that provide the sound. It is the placement of fingers on the upper reaches of the neck that determines the note the string will make. A capo may be used to raise the pitch of the guitar for an entire song. Guitarists learn special plucking patterns that give rhythm to some songs.
An electric guitar has a way to pick up the sound and then process it through amplifiers which is why most electric guitars are solid and do not have the resonating chamber of regular guitars.
A steel guitar is a variation on the electric guitar. The instrument is held horizontally on a stand. Instead of placing fingers on the strings to get a note, a steel slider is moved along the fretless instrument. The strings are then plucked with the other fingers.