keyboard - Creating a custom function key in Windows

I would like to "create" a fn key ( similar to what laptops have ) on a desktop keyboard. What I would like to do is to bind Capslock to a new custom key, so that I can add new shortcuts involving that key.
For example, remapping the jkil keys to left/down/top/right keys. So when
Capslock + J is pressed, a left arrow keypress is simulated.
I cannot bind the capslock key to an existing key like Win/Shift/Ctrl/Alt, because it will cause conflicts in my text editor because of the additional custom functionality I have within it.