I want to know how to unlock gatlin gun and others. Could someone can help me?
I assuming you're referring to modules in conquest mode.
Each city on the map has an associated bonus that goes along with it. When you capture that city you gain that bonus. Some of them unlock certain technologies that make more modules available. Others just improve various stats of existing things.
It's often useful to use spies on nearby enemy cities to learn which bonuses they have so you can prioritize capturing your favorites.
When you start a new conquest map, your unlocked bonuses return to zero and the those chosen to appear on the map are randomly selected. There are currently more bonuses than there are possible cities on the largest maps, so you'll never be able to have all bonuses unlocked at any given moment.
Hope that helps.