Click on the empty tiles to the left to construct buildings, use them to defend your base from enemy and to produce units to attack them. All structures are upgradeable, which makes either them or units they produce more powerful.
One of the best turn based strategy games. Spies, Diplomacy, Propaganda, or an all-out war with aircraft carriers and submarines. You decide. Play at 3 different difficulties and against 1,2,3 or 4 opponents.