Troops are the army of a city. They are used to defend your city, attack players, gather resources, and explore ruins. They also increase the power/might of a city. They move from one tile to another at a speed and consumes food while they live.
During a battle, the order which troops are attacked will be:
Tanks, Farmers, Damaging Infantry, Melee Cavalry, Ranged Cavalry, Bowmen, Crossbowmen, Siege Engines.
Also, troops of lower level are attacked first.
When a troop's health is reduced to nil, it will die. However, if it dies in a defence of your castle and your Hospitals have enough space, it will become wounded.