Ohm's law describes the relationship between voltage, current, and resistance in electrical circuits. It states that the current through a conductor is directly proportional to the voltage applied and inversely proportional to the resistance of the conductor. The document provides an analogy comparing current in a wire to water flow in a hose and explains how increasing voltage or decreasing resistance increases current, similar to opening a tap wider or narrowing the hose. It also summarizes the key differences between series and parallel circuits, noting that current is the same in all parts of a series circuit while both current and voltage can vary in a parallel circuit.