The current flowing in an electrical or electronic circuit can suddenly increase when a component part fails. This can cause serious damage to other components in the circuit, or create a fire hazard. To protect against this, a fuse or a device called a "circuit breaker" can be wired into a circuit.
The part of an electrical circuit that is between the electrons starting point and the point where they return to the source is called an electrical circuits "load".
Electrical and electronic circuits can be complicated. Making a drawing of the connections to all the component parts in the circuits load makes it easier to understand how circuit components are connected.
Schematics use symbols to represent components in the circuit. Conventions are used in a schematic to represent the way electricity flows. The common convention we use is from the positive to the negative terminal. The realistic way electricity flows is from the negative to the positive terminal.