All you need is to send ships from one island to another.
But there are several type of islands, and each could be used for its own purpose:
1) Colonies - produces more boats. Can be little, middle or huge.
2) Mine - produces gold for upgrades. The more population it has, the faster gold it produces. The more gold you have the more islands you could enhance and the more boats you could produce.
3) Tower - protecting everything near them by shooting at enemy ships. Shooting speed determined by level, gun power depends on tower population.
4) Shipyard - produces fast boats, perfect as anti-tower unit.
The game has 20 puzzle-based levels: you couldn't win just rushing the enemies, there is always smart way to victory, and you need to discover that. All opened to review.
The game saves finished levels and earned score.