Why do you put the resistor for the Led before the Led - i.e Digital Pin -> Resistor -> Led -> Ground
in the same example circuit above for the Switch we put the resistor after the switch before the ground. i.e 5v out -> Button -> Resistor -> Ground
I understand we use Ohms Law - So the voltage of the Arduino is 5v and the current from the pins is 40ma so using Ohm's Law we would need a resistor with the Value of 125 ohms - is this correct ?
Does a resistor use / consume the Current
Yes it burns it off as heat.
The resistor stops the LED or Arduino burning out.
I understand that the resistor is reducing the voltage in a circuit,
I expected the LED to light up much more and, eventually, to burn out; but actually it didn't happen. The only result was that the LED was not lighting up any longer.
As I trial, I tried to see what would have happened in the circuit if I removed the resistor.