These buildings are where you will be training/upgrading your troops. There are three different Troop types: Infantry, Marksmen, and Lancers.

Each Troop type has their own building where they will be trained: Infantry Camp, Marksman Camp, and Lancer Camp.

They upgrade to the level of your Furnace and are usually one of the upgrade requirements needed to upgrade your Furnace to the next level. Each upgrade increases the Training Capacity(how many troops you can train at one time), reduces training time, and boosts your power.

At certain upgrade levels, you will gain access to higher tier troops. Once you have unlocked T5 troops, you will gain the ability to promote your lower tier troops to the highest trainable tier.

Researching the technology Camp Expansion in the Growth tab of the Research Center will further increase the number of troops you can train at one time. Researching Training Tools, also in the Growth tab, decreases the time needed to train a group of troops.