A standard method of understanding the flow of electrical current is to compare it to a mammalian circulatory system. In a mammal the heart is the pump that drives the circulation of the blood throughout the whole organism, such that the blood reaches every single cell in the animal. Similarly, the wires in an electrical circuit carry the electrical current throughout the whole circuit making sure the device the current powers can function. In a circuit the power source is either a battery (or electrochemical cell) or generator which supplies mains electricity.
For electricity to be transported the circuit must be complete and a voltage or potential difference must exist. Just as when we cut ourselves, blood flows outside of the circulatory system, if the current cannot complete a circuit then electricity will not be transported and the device or mains appliance will not function. At its simplest an electrical current is a flow of electrons, which are negatively charged sub-atomic particles.
Voltage (potential difference) is the force required measured in volts to push the electrons through the circuit. Any GCSE physics text book will impart that the flow can only occur if there is a build of electrons (and therefore negative charge) at the negative (anode) terminal of the circuit. This means that there is a deficit of electrical charge at the positive anode (cathode). The flow of electrical current always occurs as a result of a flow of electrons from the anode to the cathode.
The more energy the electrons have (not necessarily the actual number of particles) determines the voltage needed to move them around the circuit. Hence the electrons in a torch have less energy than the electrons in car battery. The flow of electrons from the anode to cathode is measured in amperes. Put simply voltage and amperes can be mathematically connected to produce a unit we understand as electrical power. The greater either value is the more power produced as measured in Watts.
Resisting the flow of electricity
In the circulatory system the flow of blood is impeded by the friction generated as it contacts the vessel walls and the reduction in pressure as it is pumped back to the heart. Similarly, when electrons flow through the conducting wire there speed is reduced as they come into contact with the atoms which compose the conducting material.
The wire is said to resist the flow of electrons and the greater the degree of resistance the more voltage is needed to push the electrons through the circuit. The degree of resistance depends on the material used to create the wire, its diameter and its length. As with power resistance can be calculated through the mathematical relationship between voltage and current.
Electricity is a natural phenomenon which has become inextricably linked with the continued evolution of the human species. In short, it is a simple flow of electrons from negative to positive terminals which we simply cannot do without.