You win the battle when the opponent is at 0 HP. The way to hurt your opponent may differ between matches. In Classic Mode, you hurt enemy by having units on the field when he doesnt. Deathmatch is the same, except you also hurt him by destroying his units. In King Of The Hill, you hurt him by having control of the Hill in the middle of the map. In Capture The Flag, you hurt him by returning the flag to your side of the field. In Power Ball, you must hold onto the Power ball until he dies.
Like any other Real Time Strategy game, you must lead your troops to win the battle.
Bills aimed at restricting sales of violent games to minors are the latest salvo in a long campaign by detractors and some parent groups to limit access to games with adult content. Critics of violent games often cite research suggesting that such games can increase aggressive behavior in young boys.