The Sicilian Defence?

1.e4 c5 2.Nf3 Nc6 3. ?  . These past few weeks while playing Live Chess , I've encountered a couple of players who've answered my King's Pawn's Opening with the Sicillian Defense. At first after c5 I had only one move in my mind, Knight to f3. It was quickly answered with Knight to c6. It was then that I realized I had no idea how to play against the Sicillian Defense, I went on to go with d4 & ultimately lost the game. As my encounters the Sicillian Defense then on, I've tried many different variations and managed to win at least 4 out of 9 games. I want to know how would you answer this position, what would be going in your mind, how do you think your opponent is going to answer to your next move & do you think the Sicillian is effective against you?