2003 Chevy Venture Want to know how to address code P0131

OBDII scanner displayed a DTC P0131 which means HO2S circuit low voltage sensor 1 or particularly defined as Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 1). I just want to know what specific problem is this and how is it going to be addressed so that it won't come back to light up the MIL again. Appreciate your prompt response on this, Thank you...