In order to read a schematic, you have to learn symbols. For example, a wire is drawn as just a straight line. Two wires crossing, but not connected, is drawn with no dot at the intersection point. Two wires that connect at the intersection point show a dot drawn in at the point of intersection. The University of California demonstrates that the symbol for a resistor is a zig-zag line. The symbol for a capacitor is two short parallel lines drawn close to each other.
Learning how to read symbols is only half the battle. Learning what each component actually does is the other half. For example, a diode is a one-way valve. It only allows current to flow in one direction, similar to a one-way valve in a water pipe. The symbol for a diode is an arrow, with a short line drawn at across the tip of the arrow, perpendicular to the shaft of the arrow. This indicates the arrow stops the current. Current flow is actually opposite of the direction the arrow is pointing.
Electrical schematics in construction are similar to electronic schematics. Some terminology is used that is specific to electrical power in buildings. For example, if you see "RP" next to a wire, it stands for "Receptacle Power." If you see "LP" next to a wire, it stands for "Lighting Power." Follow a wire to all the points it connects to, and you will see it will eventually leads to the circuit breakers.
Color codes are all-important in the electrical field. For example, red stands for positive, and black stands for negative. Usually on a schematic, the color of the wire is written in beside the wire. For residential construction, black is the main current carrying wire, called the "Hot." White carries current as well, but is connected to the ground wire, usually inside the breaker panel. The white wire is called the "Neutral." Green is always Ground, and carries no current except in a accidental short-circuit situation. The ground is a safety feature. A short circuit happens when the hot accidentally touches the neutral or ground. The current is directed to the ground, and away from the main circuit. Color codes for other applications (such as marine electrical systems) are very extensive. In order to read an electrical schematic effectively, you must learn all the colors and what they stand for.
Learning how to read a schematic is not an overnight process. You must learn symbols, what the components do, and the color codes. This process may take years. Many community colleges and other educational institutions offer classes on electrical schematic reading. If you choose to go the self-taught route, read textbooks and other material on how to interpret a schematic.