What is the difference between current and voltage?

Voltage is the cause and current is its effect. Voltage is the potential difference between two points. When charges flow due to this potential difference, we say that current is flowing.

Voltage and current can be compared to a water reservoir with tubes connected to the outlet, the reservoir is the supply. Now, voltage is compared to the pressure of the water at the outlet of the reservoir, and current compared to the the volume of the water that flows through the tubes, the thicker and shorter the tubes, the less the resistance and larger the volume of water passing through the tubes. To measure voltage, a volt meter is connected across the output terminals of the supply; to measure current (in units of amperes), one of the wires connecting a circuit to to the supply is cut, and a ammeter is connected to the two ends; or if there is a switch in the circuit it can be switched off, and the current can be measured across the terminals of the switch. The best way to measure current is by using a clamp type ammeter.

Voltage (sometimes called electric potential difference) is the electrical driving force set up by an electric potential difference. There are several ways to create an electric potential difference, but in any case, it is voltage that causes current flow if there is some kind of circuit or current path to support the flow. Current or current flow is the actual movement of electrons through the branches of a circuit when voltage (the "motivational force" that causes current flow) is applied.