C dim
The C dim chord consists of the C (Perfect unison), D# (Minor third) and F# (Diminished fifth) notes.

How to play the C dim chord
- Find C (Root) on the piano keyboard
- Add D# (Minor third) — 3 semitones above C
- Add F# (Diminished fifth) — 6 semitones above C
- Press all 3 notes simultaneously to sound the C dim chord