Silver is the most precious resource in Chronicles of Merlin. Once you've gotten used to playing the game you ought to start planning your economic growth. Leveling up your Residences, occupying Silver Mines, raising your Title and completing Missions are all ways of filling your coffers
When your City reaches Level 15 you start to lose Reserves each time you do battle. The only way you can replenish your army's Reserves is with Grain. Grain is most easily obtained by occupying Farms. Click on the "Farm" button on the bottom right-hand corner of the Game Interface to occupy a Farm or to take over another player's farm. You can also Buy/Sell Grain at the Market. Grain prices vary though so try to buy when it's low and sell when it's high.