It wuld really help to know what kind of car your talking about but , generally you have multiple 02 sensors, which they are generally located under the car right in the middle.
The 1994 S10 uses a MAP sensor, not a MAF sensor. We need to know size engine you have in that S10.
After the catalytic converter.
That should be the sensor located after the catalytic converter.
That should be the O2 sensor just before the catalytic converter.
If it has a 4.3L engine the temp sensor is located next to the thermostat housing.
We will need to know which engine it has to answer that.
4.3L? Inside the distributor.
the fuel level sensor is located in the fuel tank with the fuel pump
The coolant temp sensor on a 2003 Chevy S10 V6 is located on the front of the intake manifold. To replace simply unscrew the old sensor and screw on the new one.
You won't find one. The 1991 Chevy S10 doesn't have a MAF sensor.
Inside the distributor.
Passenger side of engine block, close to the coil pack, probably easier to reach from underneath.