Gsus

The Gsus chord contains just 3 notes: G, C, and D.  The 1st, 4th, and 5th notes of the G major scale.

Gadd4

The Gadd4 chord contains 4 notes: G, B, C, and D.  The 1st, 3rd, 4th, and 5th notes of the G major scale.

Csus

Csus contains the notes C, F, and G.  The 1st, 4th, and 5th notes of the C major scale.

Cadd4

Cadd4 contains the notes C, E, F, and G.  The 1st, 3rd, 4th, and 5th notes of the C major scale.

Dsus

Dsus contains the notes D, G, and A, which are the 1st, 4th, and 5th notes of the D major scale.

Dadd4

Dadd4 contains the notes D, F#, G, and A, which are the 1st, 3rd, 4th, and 5th notes of the D major scale.

This is an especially pretty sounding shape because the F# and G are a half step apart and the G rings out as an open string. This shape is very useful as the 5th chord in the key of G Major.

The Difference Between Sus and Add4

Diagram Collection

Gsus