Have you wired up an IR decoder/detector?
My favorite library for IR remote control is the IRremote library. The IRremote library is available to install through the IDE library manager.
Try some example codes that come with the IRremote library to learn how it works.
Post a data sheet for the light or a link to information about it. Without knowing more about the light it is impossible to know how to control its brightness.
The more information that you provide about the hardware and the requirements of your assignment the more and better help we can give. We do not provide the whole solution but will help you get there.