You start in the cave age with a club-swinging caveman and a small base, and your opponent has the same. Age of War 2 is a lane-style strategy game: send your units along the field toward the enemy base, hold off the attackers with turrets and slowly climb through history.
It is all mouse clicks, so it is very easy to learn. A common mistake is spending every coin at once; leave enough to evolve in time. Plants vs Zombies is the closest relative we host, with a similar defend-your-side feel.