The continuation bet or "c-bet" is perhaps the first postflop "move" new no-limit hold'em players become accustomed to employing.
Having raised before the flop, a player will bet again on the flop and "continue" to keep the betting initiative. In many cases if a player raises preflop and has an opportunity to bet again after the flop, the player is almost expected to do so. And truth be told, c-betting is often a profitable play since more often than not the flop will not improve the hand of the player who called.
That said, if you always c-bet every time you've been the preflop raiser, you are c-betting too much and setting yourself up to be exploited by attentive opponents.