A capo clamps all strings at a fret, raising the instrument pitch while letting you keep familiar chord shapes.
One fret equals one semitone
A capo at fret 1 raises everything by one semitone; fret 2 raises by two. A C shape with capo 1 sounds as Db/C#.
Shape key and sounding key
A sheet may say “Key: Db, chord shapes in C, capo 1”. You read C, Am, G and F shapes while the sounding result is one semitone higher.
Choose by playability and sound
Lower capo positions are often convenient, but tone and singer range matter too.
Concert pitch and played shape
With a capo, distinguish the shape under your fingers from the chord that actually sounds. This prevents confusion when playing with keyboards, bass or another guitar without a capo.
Try more than one position
Different capo positions can produce the same key with different chord shapes. Choose the one that makes transitions practical and fits the arrangement sound.
Common capo mistakes
The most common mistake is sharing only the played shapes without stating the capo fret. Anyone on another instrument may then play in the wrong concert key. Another problem is using an excessively high capo just to avoid one difficult shape, making the whole guitar part overly bright.
Write down the concert key, capo fret and, when useful, the played chord shapes. That small detail prevents confusion in rehearsals and makes the sheet useful for the entire group.