After you and your friends have completed your actions in the Planning Phase, combat proceeds to the Execution Phase, where all of the Units in combat play out their orders in turn. Once all your units perform their commands, then enemies and then any allies (units that fight with you, but you don’t control) get their turn!
Combat continues in turns until one side is defeated, or until the victory conditions are met. Note that not all combats require you to defeat all your enemies! In fact, in some combats you need to pay close attention to other (sneakier!) paths to victory. These Victory Conditions are displayed at the top of the screen, during the Planning phase. Careful, if you don’t meet a certain victory condition that’s listed, you could lose the combat.