most chords have 3 notes in, the first or root (ie D in D sus 2) and two others
its the middle note thats changed here, and just like a minor changes the middle note, so does a sus.
like a 7th chord, it can sound 'unfinished'
very sweet sounding chord, play it along with D and D sus 4, easy to play as well
serious though, spend some time on theory, and how chords are built. invaluable.
****e, just re read this thread, ive probably confused you more, what a divvy!