DC Voltage is one of the most common uses of a multimeter. This is used for anything from checking the voltage at a certain part of a circuit to testing a battery.
DC Voltage is displayed a few different ways on multimeters but usually either VDC or DCV is used. Selecting a scale - The scale that you select will read up to the stated voltage (A scale of 20V would read from -20V to 20V). Most multimeters give you a choice of scales which you can use. An average multimeter may contain the following scales 200m, 2000m, 20, 200 and 1000. The scale that you choose for your reading will need to cover the voltage range that you are using but the lower scales will provide you with a higher level of accuracy.
For example, if you were testing a 1.5V AA battery you would be best using the 2000m scale. This scale will read in mV (millivolts) so 1.5V would be displayed as 1500. This scale will display a maximum of 2000 which would be 2V.
If, however you were testing a 9V PP3 battery you would need to use a higher scale. The 20 scale which would read up to 20V would be the scale to use. Polarity - The polarity isn't usually the greatest issue with DC Voltage as if you get the test leads the wrong way round all that will happen is that the screen will display a minus symbol and the voltage.