Action can be set up by adjusting the truss rod... But often times, it's a combination of bridge height and truss rod tension. The truss rod controls the bow of the neck... in most low action setups you will have a straight truss rod adjustment.... with low bridge height... A good overall setup has a little bit of relief (slight bow in the neck from the nut to about the 7th fret) with a straight heel (straight from about 7th fret on)... and a slightly lower than stock bridge adjustment. Note, moving the bridge saddles up and down will maladjust the intonation... I suggest taking your guitar to a tech to get any bridge or truss rod work done... unless you are willing to learn by trial and error... and possibly playing with a maladjusted guitar... which may sound horrendous