Okay, "trapping is for the pros" is a bit of an overstatement, but the general idea holds true. Trying to trap your opponent in poker is a very risky business that is best left to the experienced players until one gets enough poker prowess to do it successfully. An unsuccessful trap often results in bad news for the one who set it. When a player wants to set a trap he is hoping to draw in as much money as he can because he is certain he will win the hand. The problem is, especially in a game like Texas Hold?em, there are very few times when you can be 100 percent positive that you will win.
Some examples of trapping would be starting with pocket aces and hoping to draw a number of players along to the end; your aces could easily get busted on the flop, turn or river with some thing as simple as two pair. Once you hit the flop, if you are reasonably certain you have the best hand, take the pot down then. Another example would be a set or cards, three of a kind. If you have a pocket pair and the third card comes on the flop, that is a great hand; but pay attention to betting styles and what other kinds of hands could be made. If there are two or three of a suit in the flop a flush is very likely, especially if you allow the hand to go on. Trying to tease players in with medium size bets could get you outdrawn and out of luck.
There is a difference when you are playing it conservatively; such as you are not certain if your hand is the best, but it could be, and you are not getting big aggression from the other players. In such a case it is understandable to go along to see what develops, as long as you are aware you can get outdrawn.
In the end it is important to understand that trapping is a tricky thing, and if you are still learning the ropes and interested in building your chip stack, stick with taking the pot every chance you can get.