First, what is a multi-meter? The simple definition is "an instrument for measuring electrical resistance". So without getting all complicated and with electrical terms and such, basically it is a little hand-held meter that you can use to test things like batteries, light bulbs, and electrical currents.
Here is that offensive (in so many ways) light again.
To get started turn the multi-meter to AC. This stands for Alternating Current which is what the wiring in your house is. Set the dial for the next higher setting than what you are testing for. Most house wiring is 120 volt (240 volt is used on things like dryers and ranges) so on my multi-meter the next higher setting is 250. You will notice that the AC settings near the dial are in red so the readings I will read on the analog display will also be in red.
Here are some that you can purchase on Amazon.
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