Value betting draws

If i have a nut flush draw on the flop in texas holdem and i have 3 opponents and i bet, is it for value or do i want them to fold? which is better? what about against four opponents, or two? If the draw comes in 35% of the time, i get value if 4 opponents call my flop bet, but i also loose money calling a bet on the turn if my flush doesn't come in. Can anyone clarify this concept for me?