There is no provision for reaction fire as in Age of Rifles , so you can't fire at units as they cross your field of view. Offensive Fire allows the moving player to return fire and Melee allows the moving player to fight for an individual hex, usually with deadly results for one side or for both. In order to play the game effectively, you don't need much more than a common sense understanding of how these factors affect combat. Attacking uphill is tougher than attacking downhill. Being behind a stone wall or breastworks will protect you from fire.
Tired units are less effective.
Enfilading a unit results in more casualties. In other words, you don't need to memorize the exact combat modifiers to use them effectively. A subordinate leader is promoted to take the place of fallen leaders, although their ratings will generally not be as good. Given the importance leaders play in maintaining the morale of your troops, the loss of a key leader can prove disastrous. Units which fail morale checks may become either disrupted or routed.