A voltmeter is used to measure the current drop across 2 points in a circuit (given that current drop = voltage). Say you wanted to find the voltage going through a lamp in a circuit: simply place the red probe on one side and the black one on the other side. Now, you have to make sure you're reading the correct type of voltage or you could end up cooking your voltmeter: make sure that whatever is used in the circuit (AC, or DC) the voltmeter is set to use it. This would probably just be a switch somewhere. Aside from that, theres not much to say because i dont know much about the meter in question. Is it just a voltmeter or a multimeter?