I understand that a Cmaj is comprised of the notes, C,E,G. A triad of sorts. All major chords are 4-3 half steps apart, which I also understand. But what I do not understand is that, when I want to play a Cmaj chord, which strings do I strum and which ones do I not? I would think that if my 3 fingers areplaced on a C an E and a G, and I strum other notes along side the 3 that comprise the chord, than I am playing more than the chord ya? Is their some sort of concrete rule on what to strum and what not to strum than?

Thankyou for any help possible