Voltage, resistance and current are the three components that must be present for a circuit to exist. A circuit will not be able to function without these three components.
Voltage is the main electrical source that is present in a circuit. It functions in the way that a magnet does by pulling two opposing things together without allowing them to actually touch. The force that is behind the voltage is responsible for the amount of energy that is put out and received by the circuit.
The way that charges move throughout the circuit system is directly related to the resistance that is present in the circuit system. Resistance is able to prevent charges from moving around the circuit, and the charges can be blocked completely from moving when the resistance becomes closed. Conductance is the opposite of resistance and determines how easily charges are able to pass through a system.
The current of a circuit is the way that the charges move throughout the circuit. The charges must be able to move from opposite ends of the circuit in order for it to function properly. Currents can be both negative and positive, or they can be singular. Currents that are either negative or positive are considered open circuits.