The most common interactive input control for fading LEDs is a standard potentiometer. However, when you start controlling fade curves via the potentiometer wired to one analogue input of the Arduino, ...

Call it synchronicity, or manually setting a 16-bit number in an Arduino, or how to turn an OLED into a rotary dial ...

As you can see from that sketch and the circuit diagram, the LED is connected to the digital pin 13 of the Arduino. Once you verify (compile) the sketch and upload it to the Arduino board, you should ...