Current (I) is the rate of flow of charge. It is measured in amperes (A). For any component the current depends on two things: the potential difference (V) across it and its resistance (R). A larger p.d. pushes a larger current. A larger resistance gives a smaller current.
Potential difference is the energy transferred per unit of charge as charge passes between two points in a circuit. It is measured in volts (V), and 1 volt is 1 joule per coulomb. For example, if 10 joules of energy are transferred for every 2 coulombs of charge, the p.d. is 5 V.
Resistance (R) is how much a component opposes the current. It is measured in ohms (Ω). To find a resistance, measure the p.d. across the component and the current through it, then divide the p.d. by the current.