There are three resources in Blight - Gold, Mana, and Valour.
You begin each game with 1000 Gold. You use Gold to train armies and deploy heroes.
Gold is primarily produced by settlements. A settlement's daily Gold income is shown next to the Gold icon on the map. There are also some heroes (particularly Goblins and Dwarves) that can help produce more Gold.
You begin each game with 20 Mana. You use Mana to activate the special abilities of your heroes.
Mana is primariy produced by Mana Pools. Each Mana Pool produces 20 Mana per day. There are also some heroes (particularly Elves) that can help produce more Mana.
You begin each game with 20 Valour. You use Valour to capture settlements and Mana Pools.
Valour is earned by killing zombies. In Single Player, Valour is also earned by jumping ahead more than 6 hours.