Sovereignty offers two modes of battle
1) Hex-based Panzer General style battles for stacks led by Heroes
2) Quick resolution auto-battles for the majority of non-Hero stacks.
The distinction here is that most stacks will not be led by heroes. A Hero stack should be considered special and be aimed at hot spots.
Units have a number of stats like Attack, Ranged Attack, Morale, Initiative and so forth. They may have special abilities like Scout, Shackles, Flying, Venom, Dragonslayer, and so on. Special abilities apply to both tactical and auto-battles. Terrain affects movement and combat modifiers. Elves gain bonuses in Forest, Dwarves in mountains.
While in tactical battle, players may play a Hero card: a special "turn of the tide" card at a key moment. For example, let's say you're playing as the Orcs of the Iron Barony. Your Hero is a Taskmaster. The card grants: All Units you control have a -1 Morale for the remainder of this battle. Your opponent skips his next turn.
A powerful tool that comes at a cost. Use it at key moment to unbalance your enemy!