nemy troops are bound to attack sooner or later, so you'll have to keep your eyes peeled for their advances.
You can design your floating island however you like. Of course, you can only add elements that you've unlocked after winning battles against your enemies. To carry out an action, all you have to do is indicate the direction of attack and place units on the battlefield, fighting your enemies until they retreat.
This game's entertaining gameplay plus a wide range of characters and fortresses ready to be unlocked make Fortress Isles: Sky War super addictive. Beyond that, the fact that you can improve the buildings on your floating island practically guarantees hours of fun, not to mention real-time combat against other players all around the world.