You can literally take several college courses to get all the required knowledge to properly read an electronic schematic. However, there are some basic principles involved that will aid you in your quest to understand these diagrams. One use of looking at a schematic when you have not been trained about them is so that you can repair a piece of home electronics.
Wires
Every schematic is going to have some number of wires. These are typically physical wires, although they can also represent wire traces, which is a conductor deposited on a circuit board that is used as a path for electricity flow even though it is not a wire in the conventional sense. Wires are used to connect the other pieces of the circuit together for current flow.
Components
These are all the other little pieces of an electronic circuit. Typically this will include resistors, capacitors, inductors, fuses, switches, diodes, voltage sources, grounds, and microchips. There are many other possible components, but these are the most common. You can find charts at many locations online that will show you what the different symbols represent, or the schematic itself may have a legend. There will also be a number beside the component to tell you its rating.
From the position of attempting a simple repair to a piece of electronic gear, first consider the fuses, as these are designed to be the first point of failure. Most electronics stores will be able to test a fuse for you, so if your device is not working and you find a fuse, consider that the first possible problem.
Connections
If a wire goes directly into the end of a component it is considered to be connected to it. On some more complicated schematics, however, the wires might cross but not actually form a connection. The way that connections are indicated on these schematics is by a small, filled-in circle at the junction. If the wires cross but there is no circle, there is no connection.
Test Points
A few schematics may even list test points and the values that you should obtain at these points. This is to aid in diagnosing problems with the circuit. Although this is not common, it is a great aid for checking circuit function.
These are the basics of reading an electronic schematic. As there are entire books dedicated to understanding electronics and how they work, there is more material available to those who desire more knowledge.
