The unit of resistance is the ohm. Resistance is a measure of the energy that a component robs from current passing through it, and dissipates. A resistance of 1 ohm means that in order to force 1 Coulomb of charge (6.25 x 10¹⁸ electrons) through that obstacle, you need to give it 1 joule of energy. The electrons will lose that much energy on their way through the 1-ohm "resistor", and the joule will make the resistor warmer.
The unit of electrical potential difference between two points is the volt. 1 volt of potential difference means that in order to lift 1 Coulomb of charge (6.25 x 10¹⁸ electrons) to a place where the potential is 1 volt higher, you need to give it 1 joule of energy. And when the Coulomb falls down through a circuit to a place where the potential is lower, it gives up 1 joule of energy for every volt it falls through.
The unit of electric current is the Ampere. A current of 1 Ampere means that 6.25 x10¹⁸ electrons (1 Coulomb of charge) are flowing past a point in the wire every second.
