Sus4 chords are formed with the second note in the chord raised one step. In addition to sus4, there is sus2. In the case nothing more than "sus" is mention, like for example Dsus, it is normally sus4 that is intended. See also common sus chords.
The sus4 chord is very close to the original major chord because only one note is changing. A comparison of C major and Csus4:
C major Csus4
There are two differences: 1) on the fourth string the tone is raised one semi-step from E to F, 2) you don't play the highest open string since this is an E note. When shifting from C to Csus4 you only need to add the little finger (4) and you don't move the rest of the fingers.
Chord constructionCsus4 x - C - F - G - C - x
Dsus4 x - x - D - A - D - G
Esus4 E - B - E - A - B - E
Fsus4 x - x - F - Bb - C - F
Gsus4 G - x - D - G - C - G
Asus4 x - A - E - A - D - E
Bsus4 x - B - F# - B - E - F#
Guitar versions of the chord
Notes in chordCsus4 C - F - G
Dsus4 D - G - A
Esus4 E - A - B
Fsus4 F - Bb - C
Gsus4 G - C - D
Asus4 A - D - E
Bsus4 B - E - F#
The intervals are 1 – 4 – 5
A common practice is to alter the major with a sus chord, like D - Dsus4 - D.
In the Tom Petty tune "Free Fallin'" a certain chord progression is used in a big part of the song:
D - Dsus4 - D - Asus4
Another progression with sus4 chords is this one: E - Esus4 - E - D - Dsus4 - D - A - Asus4 - A - E.
Alternative chord shapes
There are some other alternative and rather common ways to plays some of the suspended chords which are presented here:
Flat and sharp suspended chords
Not so common are sus chords with root notes consisting of flat or sharp notes, but some it worth mentioning:
Rare suspended chords
As a final, some rare variations in this chord family is presented:
See also, 7sus4.