In this use case, the OPAMP0 is configured as "Non-Inverting PGA" mode, refer to the second mode of "Built-in Modes" in the device datasheet.
This use case sets up the OPAMP0 to invert the input signal in OA0NEG pin, and output it to the OA0OUT pin. You can give a signal on OA0NEG and watch the output on OA0OUT through an oscilloscope.