I might as well mention it here, by default you can't see the Civilopedia descriptions of techs you haven't yet discovered, which you can change in the BUG menu.
Regarding habitation systems, I have literally no idea what you are talking about.

It increases the population limit of the Planet it is on by 1. If you have a Planet with a population limit of 2, and you build a Habitation System there, you will have a population limit of 3 there from now on.
...
You do know how Planets work, right?
Also what surplus? Surplus population? If you have more population than can fit on your planets they are unassigned and do nothing except increasing your maintenance costs, but Habitation Systems are kind of the solution to that problem no?