All current AoC games have the same rules. All chosen actions are done when you complete a turn.
Army- Armies are needed to take over or defend a province. Armies work when you select to move it to a neighbouring province. Armies are variables with a number, in a fight, the army number is taken away (mathematically) the other army's number. The army with the higher number wins.
Capitals- All Civilizations have a capital.15% offensive and defensive bonus. If another civ has your capital for over 3 turns you lose the game. If you do the same to another civ, you will get all of that civ's owned provinces and the civ will be destroyed. All capitals have all buildings (Ports depends if capital is next to the sea) when you start the game.The capital province is identified with a crown.
Fortress- Gives a 20% defensive bonus
Port- Allows access to water provinces (only can be built in provinces bordering a sea province)
Watchtower- Allows you to see army numbers in neighbouring provinces (obsolete with Fog of War=Off)