The GM assigns the battle a difficulty, based upon how intense it is and how readily the PCs could avoid fighting if they chose.
People who choose to malinger reduce the difficulty by 3, those choosing to showboat bump it up by 3.
Everyone makes four rolls- each failed roll inflicts 1d6 damage on you, with a further +1d6 if you critically fail. Botches add an additional roll of an appropriate non-combat skill like Acrobatics. Characters who take damage may choose to surrender to the enemy afterwards, rather than continue rolling. Might lower that to d4s if it seems too harsh. YOu could take 4d6 or so generally go negative.
The base rolls are an attack for your weapon of choice (generally Melee, Thrown, Ranged or your most effective combat Spell) then Dodge and Courage. If you are leading the fight, then roll Leadership first, either vs the same diff or the Leadership of the enemy leader... on a Crit everyone gets a +2 bonus per crit, on a Crit Failure everyone is at -2 as you lead them into trouble.