The game is a strategy rpg. Those of you who have played the vastly more known Heroes of Might and Magic series will know what that is. Der Langrisser is pretty similar, though, it has a more consistent story.
You have heroes (Characters/Commanders) and units. Before battles (Scenarioes as they're called in the game) you can buy equipment and hire units for your heroes. They will level up through combat: Increase their skills, change classes, learn magic, and gain access to more and better troops. A classic strategy rpg in that respect.