Another important mathematical equation to learn is the Ohms Law, this will allow you to understand how much current is travelling trough your circuit with the equation:

I = V/R

or

Current = voltage / resistance

So 3.3 volts with 220 ohm resistance = 0.015 amps or 15 amps

Also how much resistance is needed for your circuit to run properly:

R = V/I

Resistance = voltage/current

So 3.3 volts with 15 amps = 0.22 or 220 resistor

An finally how much voltage there is

V = IxR

Voltage = current x resistance

So 15 amps with 220 resistor or 0.22 = 3.3 volts

**AMPS (amperes)**

Amps are what the current is measured in and shows how much electrical current is flowing within your circuit.

To understand amps:

1 amp = 1000 milliamps

so 10 milliamps = 0.01 amp

These can be measured by a Multimeter.