Hi ruex, as a standard keyboard normally does not have FN-keys (just Shift,Alt,Strg,Win...), you should explain your hardware a bit more
.
I guess you mean specials keys some (not all) notebooks have, but every manufacturer uses other settings and keycombinations.
For example, on my Thinkpad, Function-F5 does switch Wifi on/off, while brightness is handled via Function+Home/End. And I installed the package
tpb ('tpb - program to use the IBM ThinkPad(tm) special keys') for that.