Assuming you're new. If so its not a problem.
So the Line or spread is currently +3 for Denver at -120 which on a $200 bet pays out $367
However if you dont want the points and think Denver wins straight up or Even the odds are +120 which pays more but you dont get the 3 point spread. Its $200 bet payout would be $440. I use bovada.lv for spreads and you can use this calculator....
http://www.oddsshark.com/tools/odds-calculator