Current is the rate of flow of electrons per unit time and is measured in amperes (A). A coulomb (C) is the quantity of electricity conveyed in one second by a current of one ampere.

A load is a source of resistance that converts electrical energy into another form of energy. The components of a microwave, for example, are loads that work together to convert household electricity into radation that can be used to quickly cook food.

Direct current flows in only one direction in a circuit, from the negative terminal of the voltage source to the positive. A common source of direct current (DC) is a battery.

Connecting the 6 batteries in series multiplies their voltage while keeping their current the same yielding a 72V 15A configuration. Connecting the 6 batteries in parallel multiplies their current while keeping their voltage the same yieleding a 12V 90A configuration. Using a series-parallel connection, 3 batteries can be connected in series and 3 can be connected in parallel resulting in a 36V 45A configuration.

Resistors are used to limit voltage and/or current in a circuit and can have a fixed or variable resistance.  Variable resistors (often called potentiometers or rheostats) are used when dynamic control over the voltage/current in a circuit is needed, for example, in a light dimmer or volume control.