When a voltage is connected across a wire, an electric field is produced in the wire. Metal wire is a conductor. Some electrons around the metal atoms are free to move from atom to atom.
These electrons experience a force which moves them through the wire, causing a movement of charged particles, or current.
Electrical energy is transferred to the electrons each time they pass through the battery. The battery may be connected to a circuit with components, such as lamps or resistors. When electrons pass through the component, work is done. Some of the energy of the electrons is transferred to the component. This causes a difference in energy across the component, which is known as an electrical potential difference (p.d.)