For starter, let me say that servers and stuff like that are really not my strong point, so I'll try to explain myself as I can because I forgot the name of the thing I'm trying to do.
Let's say in my browser I type http://something
I know there is a place somewhere where I can say "something means 126.96.36.199" and then make the appropriate redirection.
What's the name of this thing? How do I set that in MacOS and Windows?