Basic LED Circuit
The first circuit we are going to make will be a basic circuit to make a LED light up.
Schematically that will look like this:
Let us go through this circuit in detail. The LED is connected in series with a 10 kΩ resistor between 5 V and GND. We know the voltage drop over the LED itself is roughly 2V (depending on color - a red LED typically 1.8V growing to about 3V for a blue LED). Since we connect the circuit to +5V we will want a voltage drop of around 3V over the resistor.