Your commands consist of Attack, Tech, and Item. Attack is to strike an enemy with the weapon you are currently equipped with. Later your characters will learn to use magic, magic is listed under the Tech command and is denoted by a star. Item obviously lets you choose to use items during battle. When you wait and let your other members speed bars fill up, the Tech command becomes the Combo command.
Combo allows two or three characters to combine their attacks to do a lot more damage.
There are special items that can be equipped which allow certain party members to perform special Triple-techs that cannot normally be learned. Crono the main character, is an aspiring swordsman who is drawn into the adventure of a lifetime. He is destined to master the magic of Lightning. If Crono's companions are brave enough they can save him from an ill fate. Marle is actually a princess whom Crono bumps into at the Millennial Fair.