Resources:

• Arduino board
• LED
• 220 ohm resistor
• hook-up wires
• breadboard

Circuit:

Connect the anode (the longer, positive leg) of your LED to digital output pin 9 on your board through a 220 ohm resistor. Connect the cathode (the shorter, negative leg) directly to ground.

For more information:

https://www.arduino.cc/en/Tutorial/BuiltInExamples/Fade