1.e4 c5 are the moves which define the Sicilian Defence. Black fights for the d4-square, but unlike with the double move of the black e-pawn the symmetry is immediately destroyed and Black is indicating that he is not simply aiming to achieve equality. Then things can continue in quite different directions. 2.Nf3 followed by 3.d4 cxd4 4.Nxd4 leads to the Open Sicilian. But before that, Black has the option of laying down the direction in which the opening will go, according to whether he plays 2...d6, 2...e6 or 2...Nc6. But nowadays systems in which White does without an early d4 are also very popular.