Some of the main features of the multimeter are: A voltmeter, an ammeter, an ohmmeter. As always one must be cautious when dealing with electricity. Make sure there is no way electricity could flow through you. Use insulated probes, and do not come into contact with anything that could allow an electrical path to you. Generally plastics and rubber offer some protection, metals are conductors, and some things you may think are not conductors may be. For instance carbon conducts electricity.
Now voltage gives some idea of the force driving current through a conductor – a higher voltage means more current will flow. As you do NOT want a high current flowing through you you must not subject yourself to high voltages.
The voltmeter measures voltage, the ammeter measures current going through something and the ohmmeter measures the resistance to current. A higher resistance means a smaller current will flow. One might think of a small water pipe allowing less water to flow than a bigger pipe.
The ohmmeter allows you to check for breaks in wires in simple some electrical appliances. The ohmmeter works as follows: A battery in the ohmmeter supplies a voltage and this drives a current through a circuit. If there is a break in a wire and you are measuring the resistance of the wire by placing a probe at each end of the wire current will not flow and the ohmmeter will show a maximum resistance. If there is no break in the wire the ohmmeter will show a low resistance. This can be used to tell you if there is a break in a wire. Make sure the simple appliance is disconnected before checking for breaks in wires – if even a fairly low voltage is applied across an ohmmeter (or a multimeter set to the ohmmeter option) the ohmmeter can blow, so unplug the appliance for this reason and for SAFETY.
Now using the ohmmeter you want to check for breaks in wires, and whether there is any any contact between wires (neutral live and earth). There must be no contact between wires when the wires are disconnected from the appliance. If the wires are connected to a device such as a kettle then the live and neutral wires are connected via the element of the kettle and a moderate resistance shows. The earth wire especially should be checked to see that it has a very low resistance as this wire can save you from a bad shock. To check properly that the wires are insulated from each other electricians use a megohmmeter (often called a megger) which uses a high voltage applied to the wires. You can’t do this, but you can do a less effective check using the plug pins and your ohmmeter. You can check to some extent to see that there is maximum resistance between live and neutral and between live and earth and so on. If the appliance is not plastic and is earthed there must be a very low resistance between the earth pin of the plug and the appliance. This can be checked with your ohmmeter.
A final word: Take care when dealing with electricity. If you are interested, why not get a book on fixing electrical appliances?