Midnite Rider's web site explains it very well.
Their are simple multi meters and complicated meters it is best to purchase a meter for your needs and level of comfort. Three most commonly use functions are AC volts, DC volts and Ohm's. AC volts most commonly are used for checking voltage in household/commercial situations. DC volts are found in automotive, tractors, etc. The Ohm meter function is for testing continuity of a circuit. checking for a bad wire or connector, or even used to test the resistance of an electric clutch against the known resistance published by the manufacturer for trouble shooting.
With all that said the easiest way to familiarize yourself with the meter is to practice on a known good voltage source to get comfortable with the meter. Try on a 120 volt AC household circuit then test you 12 volt battery to understand those functions. You can practice the Ohm meter function on any dead circuit or wire just keep in mind the circuit should be de-energized before testing. It would even be a good idea to unplug your electric clutch and get the ohm reading of it and record it in your owners manual for future reference if the case ever arises.
