Coins
Whenever you clear a stage you will be rewarded with coins, you can also earn coins by gathering them up when an enemy drops them when you defeat them. The more coins you grap the quicker you can upgrade your forces and pick up boosts for your character.
How to get $$$$ easy
To get more $$$$ easy you must at least beat the first level.then go to the settings on your device and change the day up by one.when you go back to the game you will get money.the more stars you have from levels will give you 100 more coins everyday.every time you change the date remember to touch the home screen button or it wont work.hope I could help.
Resurrecting Dead Character
When your character is killed you will be given a chance to resurrect them. Doing this will cost you gold coins and more often than not you will be better served by just restarting the level and using the strategic knowledge gained from your failed attempt to make a better new attempt.
Upgrades
Listed below are the three upgrades available in the game and their effect. These upgrades are not permanent and need to be reapplied regularly.
Spell Upgrade:
Gives a 40% increase to your spell damage.
Hero Upgrade:
Makes your hero 60% stronger and more resilient.
Troop Upgrade:
Gives you a 30% boost to your morale bar, allowing you to call in reinforcements more rapidly.