electric current

If voltage is the water pressure, electric current is the actual flow, how much charge streams past a point each second. In the pipe picture, current is the litres per second rushing through; a fat pipe under high pressure carries a strong flow, a clogged thin pipe only a trickle. In a wire, current is the river of electrons moving along. No complete loop, no flow: charge needs somewhere to go.

Current is measured in amperes (amps, symbol A). One amp means one coulomb of charge, that 6.24 x 10^18-electron pile, passes a point every second. Small electronics live in milliamps (mA, thousandths of an amp): an LED runs on about 10 to 20 mA, a microcontroller a few mA, while a kettle pulls around 10 A. By long convention, conventional current is drawn flowing from plus to minus, the direction a positive charge would move, even though the actual electrons in a wire drift the opposite way. It is a harmless historical quirk; just be consistent.

Current is what actually does the work: it heats the kettle, lights the LED, spins the motor. It is also what hurts you in a shock, because it is current through the body, not voltage alone, that is dangerous. The same current flows all the way around a simple loop and does not get used up, a fact that trips up beginners; the energy is spent, but the charge keeps circulating. Current, voltage and resistance lock together through Ohm's law.