A digital ohmmeter has two probes. When the probes are touched together, the ohmmeter should read zero or close to zero.
The resistance of an electrical component can be measured by placing the ohmmeter probes across the component. The power to the circuit should be switched off, so that energy is supplied by the ohmmeter itself, via an internal battery, rather than the circuit to which it is connected.
The ohmmeter develops a small, known voltage between its probes and, when connected across a resistor, a current flows. The resistance is calculated using Ohm's Law, which states that voltage is equal to the product of current and resistance.