Bank one and two refer to the different sides of the engine, a bank of cylinders on each side of a V8, or V6 etc. And sensor one refers to the oxygen sensor before the catalytic converter, sensor two after the cat, so on a "V" engine you have 4 sensors, two each side. Any of them not functioning correctly can trigger VSC check. Actually, loads of different faults can trigger it but they are perhaps the most common.