**1. Basic Quantities:**

* **Charge (Q):** The fundamental quantity representing the amount of electricity. Measured in Coulombs (C).

* **Current (I):** The rate of flow of charge. Measured in Amperes (A).

* **Voltage (V):** The potential difference between two points in a circuit. Measured in Volts (V).

* **Resistance (R):** The opposition to the flow of current. Measured in Ohms (Ω).

* **Power (P):** The rate at which energy is transferred. Measured in Watts (W).

**2. Relationships:**

* **Ohm's Law:** Relates voltage, current, and resistance: V = I * R

* **Power Law:** Relates power, voltage, and current: P = V * I

* **Energy (W):** The amount of work done. Measured in Joules (J). W = P * t (where t is time)

**3. Key Concepts:**

* **Direct Current (DC):** Current flows in one direction only.

* **Alternating Current (AC):** Current periodically changes direction.

* **Capacitance (C):** The ability of a component to store electrical energy. Measured in Farads (F).

* **Inductance (L):** The property of a component to oppose changes in current. Measured in Henrys (H).

**4. Units and Conversions:**

* **SI Units:** The International System of Units is used for most electrical quantities.

* **Conversions:** Often necessary to convert between units (e.g., milliamps to amps, kilowatts to watts).

This is a basic overview. For a deeper understanding, explore topics like circuit analysis, electromagnetic theory, and power systems.