You play as the rookie commander of the human alliance fleet, tasked with defending orbital platforms against the assaults of a mysterious new enemy. Each platform is equipped with the ability to build defensive towers and you must decide where and when to build towers to successfully defend mankind from these weird aliens.
Each level of Helix Defense 2 offers a unique challenge to the player. Some levels the enemies will always travel down a certain path, but in others you have the chance to manipulate the enemies how you like. Sometimes you can even force the enemies into environmental dangers, such as molten lava.
The enemies aren't going to make it easy for you, however. Armed with shields and capital ships, they won't stop until either humanity or their own kind are destroyed.
Simply use your mouse to select a tower from the bottom right, then place it on the map area. Simples!