The probes touch the circuit, and there is no useful information on the display. The display could read zero, show the overload icon, or cycle through fluctuating values. Before testing the component, consider the multimeter itself. You need to know what the multimeter has been set to receive, from the function, the input port, and the range. Connecting the meter correctly with a wrong setting can still give you a useless reading or even blow a fuse inside the meter.
First identify what you want to measure. Different parameters such as voltage, current, resistance, and continuity have different requirements. You measure voltage across two points in a circuit that is live. Resistance and continuity are measured with the circuit dead. Current is different in that the meter is placed in series into the circuit, and the circuit is broken to accommodate the meter. If you connect the multimeter in parallel on the wrong setting, you can effectively short-circuit the power source.
The multimeter ports are also significant. Generally, the black lead is plugged into the COM port, whereas the red lead is plugged into the V/Ω port for measuring voltage, resistance, and continuity. Often there is another port labeled with either A or mA for measuring current. If you forget to unplug the red lead from the current port, you run the risk of connecting the multimeter in parallel on the wrong setting the next time you measure voltage. Be sure to unplug the red lead and return it to the V/Ω port after measuring current.
The range selection determines the span of values the multimeter can read. Some multimeters automatically select the appropriate range, though they may take a moment to stabilize. Other multimeters require you to select the appropriate range manually. If you don’t know the range of the signal you expect, pick a range that is slightly higher than your expectation and then step down until you get a reasonable reading. If you start at a range that is too low, you may see the multimeter overloaded. If you leave the range at too high of a value, you may miss small variations since the resolution is not great enough.
To try out a few of these concepts, use a small battery. Ensure the black lead is plugged into the COM port and the red lead is plugged into the V/Ω port, and select DC voltage since a battery is DC. Pick a range that is higher than the voltage of the battery. Place the black probe on the negative terminal of the battery and the red probe on the positive terminal. Record the reading and the units. Switch the probes around and note that the minus sign appears instead of the multimeter showing an error. Do the same on a lower range and see how many more significant figures appear.
Before performing any measurement, tell yourself out loud or write in your measurement log: what you are measuring, whether it is AC or DC, the range you expect, the multimeter ports used, whether the circuit is live or dead, and the connections. Take special care to ensure the multimeter is in the correct mode before measuring resistance or current. Don’t attempt to measure resistance or continuity on a live circuit, and don’t play around with line voltage when starting out with a multimeter. The multimeter is best used when the settings are considered a part of the measurement, not something you decide after the probes have been placed on the circuit.