You start with 2 extra lives.
Last man standing wins the round.
In between rounds you buy weapons, ammo etc, etc. The main object is to win as many rounds as possible, though you often care a lot more about getting money. As you buy things you grow mightier and it gets easier to earn more money, especially by destroying tanks. If you want to know more you can either keep on reading or download the game. The object of the game is to win as many rounds as possible.