The Ground is the place where recruited units stay, while they wait to go to battle.
The bigger the Ground's capacity, the more units you can take to battle, so upgrade your Grounds and build new ones in order to increase your army. Note that humans, swarm, and ancients cannot share the same Ground. Different troops require different conditions, so you’ll have to build and upgrade a separate Ground for each race.
Before you can hire troops for your army, you’ll need to build a Recruiter, which is where you recruit troops for battle. Higher level Recruiters will allow you to recruit stronger troops. With multiple Recruiters, you will still be recruiting troops from a single window. However, more troops will be trained simultaneously, so your army will be built more quickly. Just keep in mind that lower-level Recruiters are unable to train stronger units.
Barracks are where you spend resources to upgrade your troops once they’ve gained enough experience in battle. If your units don’t have enough experience to train for the next level, don’t despair; you can always purchase any missing experience from Lee the Merchant.
The Lab is where you build ammunition, which will give you an additional advantage in battle. To start production, select the Lab, click the ‘Ammunition’ button, then the ‘Production’ tab, and select the ammunition you wish to produce. Once produced, the ammunition is transferred to your arsenal. By choosing the ‘Arsenal’ tab, you’ll be able to see what ammunition you have available, and pick which one to take to battle with you. If you change your mind and decide not to take that particular type of ammunition to battle, simply click on it to return it to your arsenal. If you don't need a type of ammunition anymore, or just wish to free some room in your arsenal, you can always sell it under the ‘Sell’ tab.
Some of the most valuable upgrades cannot be built inside the Lab or Barracks, as they require special equipment that can only be found inside the Tech Lab. So, you definitely need this building if you want to upgrade certain troops and ammunition.
Upgrading your troops and ammunition is usually not rocket science. But sometimes you actually need space technology, which is why you’ll need to build a Space Lab in order to access certain troop and ammunition grades.