Action points are a resource that limit the amount of things you can do per turn in GambCiv.
How to getEdit
Constructing huts increases your number of citizens. Each turn, you get one one action point per citizen that you have.
Nearly every thing you do in GambCiv will cost one action point. This is so that turns keep flowing. One player cannot build for an hour in multiplayer and make the other players wait. Games will end up being the same length, but the turns will rotate more frequently.
Each turn, the game resets your citizen count to five. Then it counts how many huts you have. For each one it adds (25/citizens) to your number of citizens. Wesnoth drops everything after the decimal point.
If you own four huts, that ends up working like this: