At its heart, electricity is about the movement of tiny charged particles called electrons. To control this movement and make it do useful things, like power a phone or light up a room, we need to understand a few key concepts. Think of electricity flowing through a wire like water flowing through a pipe.

Voltage, measured in volts (V), is like the water pressure in the pipe. Higher pressure means more force pushing the water along. In an electrical circuit, a battery or a power outlet provides the voltage.

Current, measured in amperes or amps (A), is like the flow rate of the water. It's the amount of charge passing a point per second. More current means more electrons are flowing.

Resistance, measured in ohms (Ω), is like a narrowing in the pipe that restricts the water flow. Components called resistors are designed to have a specific amount of resistance. Everything in a circuit, including the wires themselves, has some resistance.

These three concepts—voltage, current, and resistance—are tied together by a fundamental rule called Ohm's Law. It states that the current flowing through a conductor is directly proportional to the voltage across it, as long as the temperature and other physical conditions remain unchanged.

This simple relationship is the key to analyzing most circuits.

Here, $V$ is voltage, $I$ is current, and $R$ is resistance. If you know any two of these values, you can find the third. For example, if a 12V car battery is connected to a headlight with a resistance of 3Ω, we can calculate the current:

While voltage, current, and resistance describe the state of a circuit, power describes how quickly it does work. Electrical power is the rate at which electrical energy is converted into another form, such as light, heat, or motion. Power ($P$) is measured in watts (W).

By combining this with Ohm's Law, we can also express power in terms of resistance:

Circuits are paths for current to flow. The two basic ways to connect components are in series or in parallel.

In a series circuit, components are connected end-to-end, forming a single path for the current. The same current flows through every component. The total resistance is the sum of all individual resistances ($R_{total} = R_1 + R_2 + ...$).

In a parallel circuit, components are connected across the same two points, creating multiple paths for the current. The voltage across each component is the same. The total resistance is found using the formula $1/R_{total} = 1/R_1 + 1/R_2 + ...$.

For more complex circuits, we need two more rules, known as Kirchhoff's Laws. They help us track how current and voltage behave throughout a circuit.

Imagine pipes of water meeting at an intersection. The total amount of water flowing in must equal the total amount flowing out.

Think of it like walking around a mountain and returning to your starting point. The sum of your climbs (voltage gains from a battery) and descents (voltage drops across resistors) must equal zero, because you ended up at the same elevation where you started.

These foundational concepts—voltage, current, resistance, power, and the laws of Ohm and Kirchhoff—are the essential tools for understanding and working with any electrical circuit.