Reply to building a controller, need help

Hey everybody, I am currently working on a controller and i want to try something Ean did in the DIY MIDI controller review,
You can see in the video that Ean put a LED there and the knob controls its value, I have tried to do it but i guess I'm doing something wrong,
could anyone please shed some light on this for me?
I have tried to connect the voltage from the pot to the voltage on the brain and then what about the ground?
should there be any other settings in the program?
please help
thanks for any answer!!