A capo clamps down the strings of a string instrument at a specific fret position. A capo is used...
The capo increases the pitch of your instrument. When a capo is placed at the 3rd fret of your instrument the chord shape of an A major chord will produce the sound of a C major chord.
Playing the chord diagrams on a higher pitched instrument (i.e. with a capo) means that the entire song will be played in a higher key. If you want to learn how to play the song in the original key while keeping the capo, you need to update the chord diagrams. In Song One you have two options:
Song One automatically adjusts the tuning of the virtual fretboard and updates all chord diagrams of the song.
The A major chord now shows the chord shape that will produce the sound of an A major chord (with the capo at the 3rd fret position).
The chord diagrams may also be updated by transposing the song. This approach is used by apps that rely on pre-defined chord diagrams like OnSong. The method produces the correct chord shapes but has a few shortcomings (see image).
This makes it a less desirable option to use in Song One. To use it nonetheless:
Example: Recording an A major chord without a capo.
As an example place the capo at the 6th fret position to record a brighter and lighter sounding A major chord:
Example: Recording an A major chord with a capo at the 6th fret.
The 'A dominant 13th' barre chord played without a capo.
The 'A dominant 13th' chord played with a capo at the 5th fret.