Using a Capo is a great way to raise the pitch of the guitar without having to use the tuning machines to tighten the strings. In standard tuning (A440) from the thickest string to the thinnest string, we have E, A, D, G, B, E as our notes in the open position. When a Capo is placed on the first fret the notes are raised by one-half step/one semitone to F, A#, D#, G#, C, F.
Raising the pitch another half step/semitone by placing the Capo on the second fret now gives us the notes F#, B, E, A, C#, F#. This same principle continues all the way up the fretboard, because the higher you place the Capo on the fretboard of the guitar the more the pitch is raised, and once you arrive at the twelfth fret you have reached the octaves for notes E, A, D, G, B, E. At the twelfth fret everything repeats in a higher register.
The Capo in a sense replaces the nut and adjustments have to be made where playing chords are concerned. In the open position G Major, C Major and D Major can be played with the ring finger holding down the root note of these chords on the sixth, fifth and second strings of the third fret. However, if the Capo is placed on the second fret the same fingerings can no longer be used for these chords, so the next closest option for playing G Major and C Major would be a standing, full or half Barre fingering.
Where D Major is concerned the same fingering that was previously used to play C Major with the ring finger holding down C on the fifth string third fret, which gives us open notes in the C Major chord moves up to the fifth string fifth fret, and a D Major chord can now be played.
While there are different types of Capos out there to choose from including those that are quick release I really don’t have a preferred Capo per-say, but unless one plans on heavily utilizing a capo then the ones with a strap that fasten around the guitar neck are sufficient.
To see how a Capo is used watch the following VIDEO