There are two common types of Suspended chords: Suspended 2nd (sus2) and Suspended 4th (sus4). The Suspended 4th chord is the most common and is often referred to simply as a Suspended chord (sus). This creates confusion, and improper usage of the term Suspended is common, so if you run across a chord such as “Dsus” try a Dsus4 chord first, and if that doesn’t sound right try a Dsus2.
Suspended chords have an ambiguous sound that is neither Major or Minor. This is because they contain no 3rd note, the note which determines whether a chord is Major or Minor. Suspended chords have a 4th or 2nd note in place of the 3rd.
Suspended chords are often used to “flavor” major chord progressions and can accompany or replace a Major chord in a progression.
Here are the open Suspended 4th chords:
Here are the open Suspended 2nd chords:
Here are Supended 4th and Suspended 2nd Barre chords:
You should eventually memorize all of these chords, but the most common ones by far will be the Dsus4, Dsus2, Asus4, and Asus2. So start by memorizing them.
The following chord progression shows how Suspended chords can be added to D and A chords to make a more musically interesting progression.
Hint: when playing the Dsus4 chord simply play a D chord and add your 4th finger (pinky) to the chord at the 1st string 3rd fret. Since your pinky will be in front of your 2nd finger (middle finger) you don't need to take your 2nd finger off the string. Then you can simply remove your pinky and have a D chord again.