Watch the Clearing Capo Confusion online guitar lesson by Rich Maloof from Guitar 201: Breakthroughs
Putting a capo around the fretboard is like adding a fixed barre across all six strings or moving the nut up. Capos are great for instantly changing key (for example, to accompany a vocalist’s range) and for creating higher-register guitar parts. Just beware when reading a chart or talking about chord names, because it gets confusing. Like barre chords, the capo shifts the harmony around the neck. For example, a chart may call for an open D chord with the capo on the 3rd fret. You will still fingering that familiar D shape from open position, but that ain’t a D no more. With the capo on 3, it’s an F. Again, like a barre chord you can reference notes along the 5th and 6th strings (see chart) to figure out the real name of the chord you’re playing in front of a capo.