Alternatively called a circuit analyzer, multitester, or VOM (volt-ohm milliammeter), a multimeter is a device used to test and measure current, voltage, and resistance. The picture shows an example of a digital multimeter. The multimeter connects to a circuit using two (red and black/positive and negative) probes.
Before testing any electrical component with a multimeter, properly ground the system and yourself. Leave the device plugged into an electrical wall socket if the outlet is grounded.