i'm in one of the tutorial scenarios : how do i build a church ? do i have to get prestige points, then unlock the church or what ? thanks
Yes, you need to unlock the Stronghold, Export Office, and Church - it is the middle one in the first row. Some maps start you off with enough prestige points so that it costs you nothing. The shortcut key for the church is G.
If you are playing "A Formidible Adversary" you start out with enough prestige to unock 3 things.