The Structure of the Acoustic Guitar
Six strings, each with a higher pitch

Guitars typically have six strings. Each string has a different thickness. Starting from the thinnest string, the strings are called string 1, string 2, and so on, up until string 6. Strings 1 and 2 are called "plain strings" and are bare steel strings (unwound). Strings 3 through 6 are wound with metal. When holding a guitar, string 6 is the topmost string.

Moving from up to down (i.e. from thicker to thinner) result in an increasingly higher pitch. The diagram below shows ordinary tuning, which refers to the tone produced from each string when not held down with the left hand.

As strings become shorter their pitch increases. Guitars are designed to use this property so that the pitch they produce increases a semitone each time the position the string is held down at changes.
The metallic parts on the neck are called frets. A player uses his or her left hand to hold the strings down in the spaces between the frets. There are a total of 20 frets for 20 semitones. This means that, for instance, string 6 can play from low E to C on the second octave (weak). However, the strings can be difficult to press nearer the sound hole, so this area is not often used.