Bank 1 is the side that has # 1 cylinder in it, the sensor is located in the exhaust head pipe before the Cat Converter, one note of caution: an O2 code does not always indicate an O2 sensor problem, it depends if the code is a lean code or a rich code, lean may may be a sensor, rich is never a sensor, lean codes can be caused by all kinds of issues, a bad MAF, a vacuum leak from hoses or a leaking intake gasket, an injector problem and so on. Good luck hope it is the sensor.