A multimeter is a common test device that can measure electrical parameters such as current, voltage, resistance, etc. Here's a simple tutorial to teach you how to use it::
Determine whether you need to measure current, voltage, or resistance.
Rotate the dial plug to the desired amount (e.g. DC or AC voltage, current, resistance).
If you're not sure how much voltage or current you need to measure, choose the highest range and gradually lower the range until you get a good reading.
If you are testing voltage or resistance, plug the black (COM port) and red (V MA port) probes into the corresponding connectors.
If you are measuring current, insert the black wire probe into the COM port and the red wire probe into the corresponding current level port (e.g. 10A or other).
When measuring voltage or resistance, place the red and black wire clips of the probe on both ends of the component to be measured.
When current needs to be measured, a multimeter is connected in series to the circuit. That is, open the circuit and connect to the multimeter.
Read the values on the dial.
Note that overloading the circuit during the measurement process should be avoided to prevent damage to the multimeter or circuit.
After use, remember to turn off the multimeter and remove the probe to prolong battery life.
The multimeter may be a little different for each brand and model, but the above steps should work for most common types of devices. Before you start, it's a good idea to read the user manual and make sure you know how to test safely. Electrical equipment can be potentially dangerous if used incorrectly, so be extra careful!