In the Training Camp you will be able to train new types of soldiers and other military units. Depending on how many you have, you can use them to your advantage. When you want to train them, you should always keep in mind their traits, because some units have more advantages in battle versus other units.

Barbarians are strong against Archers.
Archers are strong against Riders.
Riders are strong against Barbarians.
Barbarians, Archers and Riders and strong against Catapults.
Catapults are strong against Plants.

So whenever you see an enemy and you know what type of fighters they have, try to counter pick so you will always have the upper hand in a fight.