What is a capo?

A capo is a clamping device that is laid and tightened across the neck and strings of a guitar (lute, banjo, mandolin, etc.)--in essence moving the nut.

How a Capo Works

Using a capo physically (but not literally) shortens the strings and therefore raises their pitch. This is called transposition and allows the player to use first position chord fingerings from one key to play in another.

What's That Look Like?

Let's say you know the following first position chords: E, A, and D and you have a piece of music that uses the chords G#, C# and F# which you don't know or which are difficult to finger in the first position. By placing the capo across the fourth fret the song can be played above the capo as if you were playing at the nut in the key of E, but tonally it will be in the key of G#.

Another Application

Maybe the song, as written, say in the key of C is too high or too low for you to sing along with. You want to sing, but you want to play it using the chords you know. from the key of C. All you have to do is find the right place for the capo on the neck. Though the pitch of the strings is higher, you can sing an octave lower.

Capos Make You Capable

Think of a a capo as a device that makes you capable of doing things you might not otherwise be able to do. It just makes things easier sometimes.

Source:

A Source for Guitar Players

An Organization Deadicated to New Players