Simply put, the C-Bet is when you raise pre-flop then follow up on that raise by raising again after the flop, regardless of what your hand is or if it was improved on the flop. This strategy takes advantage of your aggression pre-flop and continues it over the flop.
The goal with the c-bet is to be very aggressive and represent a strong hand to try and scare your opponents to fold, thus, avoiding showdown. This differs from a value bet as you do not want your opponents to call your c-bet. Pre-flop, you show aggression by not limping or calling but raising the pot instead. Post-flop, you follow up that aggression by raising again and hoping your opponents fold.
The c-bet should be done a high percentage of the time. The reason is that a lot of poker players in the lower stages of the game make a lot of beginner mistakes before the flop and usually call raises with weak or marginal hands. These beginners do not want to fold weak hands and often miss the flop, leaving them with the option of either a bluff or a fold. With all the dead money in the pot, an aggressive re-raise usually gets everyone to fold and gives you the win.
The best time to c-bet is when the flop has helped your hand – or when it seems that the flop has helped your hand. When you raise pre-flop, the opponent is likely putting you on big cards. When these big cards appear on the flop, you can represent a strong hand and induce your opponents to fold by c-betting.
It would also be a good idea to c-bet when a flop that helps neither you or your opponent falls. The reason being that your pre-flop aggression means you had the best hand then, and if the flop helps neither of you, then you still have the best hand.
A c-bet when playing heads-up is also good. Your opponent will miss the flop a lot more often than he hits and a raise will most likely induce a fold.
A bad situation for c-betting is when the flop likely has helped your opponent and gives him a reason to call your bet. Your goal with the raise is to avoid showdown and win the pot easily, so raising here would mean you are just throwing money away, as your opponent will likely call.
Another bad situation is when the flop gives opponents a lot of draws, like when the flop gives someone a combo straight and flush draw. There is a very big chance that your opponent has hit something with this hand that raising him will probably be a bad play.
A multi-way pot is also not an ideal spot for a c-bet. The more players there are, the lesser your chances of having the best hand. Additionally, the raise that you will make will have to go through a lot of players and someone is bound to call it.