A capo is a clamp-like device that you can use with certain stringed instruments, such as the mandolin, guitar and banjo. When you attach a capo to your mandolin's neck, you raise the pitches of the strings because you have shortened the length of string that vibrates when you play the instrument. Many musicians use capos if they are playing a song that has difficult or unfamiliar chord structures. A mandolin capo chart tells you in which keys you will be playing if you capo a certain fret and play a certain chord on the instrument.
Look for a chord that is comfortable to play in the section that says something like, "chord that you finger/play."
Look at the portion of the chart that has numbers. These numbers indicate the fret in which you clamp the capo.
Observe the point at which the chord you are fingering and the fret in which you are placing the capo intersect. This intersection indicates which chord will actually be sounding. For example, if you finger a G chord with the capo at the second fret of the mandolin, you will actually be playing an A chord in terms of sound.