HO2 sensor P1133

99 Chevy Blazer 4WD

Got the SES code P1133 - Heated Oxygen Sensor (HO2S) insufficient switching Bank 1 sensor 1.

Which O2 sensor is that and where is it located specifically?
How do I test an O2 sensor? I know it needs a multimeter and I'm good with the meter, but am I pulling the sensor and checking ohms across it?
How much resistance should there be (generally)?

Thanks for the help guys