A single stage trigger will feel like the trigger on any rifle: as you pull the trigger there will be no slack or creep, and when you squeeze the trigger a fraction of an inch the gun will fire. Some single-stage triggers are set at a higher pull weight to prevent accidental discharges, some as high as 6 lbs.
A two-stage trigger has a take-up or slack portion against mild spring resistance before you feel contact with the trigger mechanism. Once you feel contact, the pull weight is only 3-1/2 lbs and a small additional squeeze will fire the gun.
Which one is better? I'm not sure. I shoot a Rock River Arms National Match A4 configuration AR15 (NM-A4) with a two-stage target trigger (supposedly RRA makes one of the best), and I like it a lot. I shoot with one guy who has a Jard single-stage trigger in his AR, and he says he likes it but always seems to be complaining about it. I fired his AR and it would take some getting used to after shooting a two-stage trigger as long as I have.
You could talk to DPMS about having the trigger adjusted, or see a gunsmith. An aftermarket two-stage trigger will usually drop in, if you decide to go that route. Aftermarket triggers are available from Midway and brownells.