There are three main forces when using electricity, voltage, current and resistance.
Each one of these forces combined with another will influence the third one. For example, where there is little resistance, there is more current flowing through a circuit. There forces can all be measured or calculated using Ohm's Law.
V = I x R (volts = amps x ohms)
I = V / R (amps = volts / ohms )
R = V / I(ohms = volts / amps )