All circuits require an electric current to work, this is the flow of electrically charged particles. The rate at which current flows through a circuit is measured in amps.
In order for current to flow, there needs to be a potential difference between two points. This is measured in volts. If the positive terminal of a battery is 5v and the negative terminal is 0v, the potential difference is 5v. As long as the potential difference is above 0, current will flow.