C sus4/D#
The C sus4 chord consists of the C (Perfect unison), F (Perfect fourth) and G (Perfect fifth) notes, with D# as the bass note.

How to play the C sus4/D# chord
- Play D# as the lowest bass note in the left hand
- Find C (Root) on the piano keyboard
- Add F (Perfect fourth) — 5 semitones above C
- Add G (Perfect fifth) — 7 semitones above C
- Press all 4 notes simultaneously to sound the C sus4/D# chord