Silver is the main currency in Senatry.
Silver is used to develop your city, increase the Regional Prosperity, train your heroes, buy white and green equipment, upgrade equipment, and purchase crops.
You can gain silver from Levying, Commerce, Domains/Domain Wars, Vassals, Quests, and Roulette, or from selling boss drops, quest items, and crops.
Note: Capturing a Domain and participating in a Domain War event are both called the same thing in-game. It can be a bit confusing when you see first this in the Daily Quest tab.