Playing poker isn't easy as roulette and many times players need to wait a long time before they are dealt with a good hand, but waiting for such a long time might be very frustrating and that's where bluffing enters the picture. Bluffing is the most basic poker skill which is basically lying, but with style.
Bluffing is deceiving your opponents, making them think that you hold a hand which you don't really have. For example, when you hold a really strong hand you can play as if you have a low hand – only call without raising – and your opponents will believe that can easily beat you, they would raise the bets in order to make you fold, but in the end they'll have a serious surprise at showdown when you'll reveal your winning hand and take the pot to yourself.
But bluffing can also go the other way – you can bluff that you have a really strong hand by raising and re-raising your bets and all your opponents will fold without even going all the way to showdown – you'll win the pot without revealing your cards.
But there are more to bluffing than these and in fact it's a huge issue that needs time and experiences before it can be fully utilized.