Modulation refers to the modification of a carrier wave to accommodate a signal. In Amplitude Modulation (AM), the carrier wave has its amplitude varied in correspondence with the signal. In Frequency Modulation (FM), the carrier wave has its frequency varied in correspondence with the signal.
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.