Troops are foot soldiers used in battles to attack enemies. Like Heroes, they, too, come in different Elements and can be leveled up for increased damage.
You can acquire Troops by completing levels and Summoning them through the Summon Gate. Troops are equipped to Heroes of corresponding Colors by selecting the Troop in the “Edit Team” view.
Troops can be upgraded in Barracks, an Advanced building which becomes available once your Stronghold has been upgraded to level 10. Once the Stronghold has been upgraded, you can start converting a building that is over level 5 and offers you the option to 'convert' to Barracks. Leveling up Troops behaves similarly to that of Heroes, meaning Barracks can be used to get rid of any extra Troops you might have.