The Classical Variation (so called due to it's immense popularity) is often reached via 2...d6: 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 Nc6 6.Be2.
Black sometimes reaches the same position by swapping his second and fifth moves. Then it goes: 1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 d6 6.Be2, giving the same position.
The lines springing from it could have been covered in either of two sections so I'm talking about them here as there is more room. The Classical Variation was the Main Line of the Sicilian up to the 1920s or 30s. It's still pretty solid today.
Since then theory in the Sicilian has ballooned and the Classical Variation itself grew into several major variations. Black found ways to counteract it's effectiveness. There was 6...e6, the Scheveningen Variation, 6...g6, the Dragon Variation and 6...e5, the Boleslavsky Variation.