Digital Multimeters: Voltage
Voltage is the measure of electrical push moving electrons through a conductor. An electrical pressure difference exists when there is a mass of electrons at one point and a deficit of electrons at the other. Voltage meters measure this difference. They can be analog or digital. A digital multimeter will measure electrical properties like voltage, resistance and current.
High end multimeters usually have an auto ranging feature. They will have a single DC position and will automatically find the best range for the voltage measurement. A manual meter has more setting options and you just have to set the meter to the lowest range setting that does not "OL" or over-range the meter. It will also have AC and DC voltage settings. For testing an automotive 12 volt battery that will usually be the DC 20V setting. If the leads are reversed using a digital meter the polarity is changed resulting in a negative voltage reading.