To save batteries, wear on the meter and also for personal safety the standard practice for all tests using multimeters is:
To connect the leads.
Then select the function you need for a test.
Set up any extra jumper leads if needed for the test.
Lastly turn on the meter.
AC Voltage: Wall outlet or surge bar
The smaller slot is the 'Hot" and larger slot is "Neutral". Insert a lead into the 'Neutral" and one in the 'Hot". The reading should be about 110-120 volts US. Insert a lead into the "Ground" and one in the 'Hot" the reading should be almost same, if not then the outlet or bar doesn't have a good ground (not safe). Next insert a lead in the larger slot, "Neutral" and "Ground", and get a reading of no or few volts. A reading of 5 or more Volts is a real problem known as feedback, and is very unsafe for you or electrical devices.
Neutral, Hot & Ground (1) Meter reading of hot to Neutral, (2) Reading of Neutral to ground.
DC Voltage: Power Supply Unit
Insert the black probe to black (ground), then the red (+) probe to the one to be tested. If a minus (-) shows in the display, the voltage is higher on the black lead. You should get a reading that doesn't fluctuate much. If this doesn't register a reading, one that is off or fluctuating use a polarity test to get to the problem. This is great for checking a rewire mod that reroutes wire behind the motherboard, new fan extensions, or custom switch/bus bay before hooking things to the new parts.
Black and yellow molex connectors reads at 11.47 Volts DC.
DC Polarity Check: +/-
Touch the black (ground) probe to the metal case of a PSU and then the red probe to the test point. This will show a reading of true voltage from the test point. As with the DC Voltage test readings should not fluctuate much. With a 7 volt mod you test for voltage of 7volts, but with polarity test one line shows 12 volts and the other line shows 5 volts. Polarity is the proper test for a PSU motherboard connector to show the volts of each line to the Motherboard. Testing like this can find bad or loose connectors or search for power needed for LED's and such.
PSU as ground and red molex read 5.03 volts.
Black to ground and red to black molex shows that there is a little feedback, but nothing to worry about.