The Capo is a popular device used to shorten the strings of a guitar in order to raise their pitch.
Using a capo changes their tuning allowing you to easily change a song’s key without playing any differently on the neck.
The capo essentially becomes the end of the neck and all chords and scales are played in relation to it.
There are various types of capos available. Choose one that is easy to use, doesn’t get in your way and holds the strings uniformly without affecting the tuning of your guitar.
Notice how easily a G Major chord can be turned into an A Major or D Major chord simply by adding the capo on different frets and treating it as the end of the neck.