current - the amount of charge flowing past a point per unit time, units of Coulombs per second.
charge - harder to "define" as such, just some fundamental property of certain particles that causes them to respond to and affect an electric or magnetic field in the same way that particles with mass will respond to & affect a gravitational field. Measured in Coulombs.
potential difference - it is the energy required per unit of charge to move a charged object between two points in a region with an electric field. Units of Joules per Coulomb, or Volts.
I think a simple, intuitive way to think about potential difference/voltage is to imagine water in pipe. The water represents a current in a wire. Lifting the pipe at one end so that the water flows down a steeper slope would be like increasing your potential difference between two ends of your current-carrying wire.
Last edited by SnoochToTheBooch; 31-03-2012 at 18:59.