Stamina dice have faces like reroll a die, boost other die, boost during move phase.
So if you roll shit you can use stamina, or if you;re feeling luckily, had a good roll, you can use stamina die to boost to get an even better result.
Late game abilities, as well as certain weapon and armour abilities will consume stamina.
You have to recover stamina dice etc.
for example, to use a basic attack, after you roll, you must have a basic attack, dexterity and move roll.
For an ability like 'precision strike' you have have two good dexterity results, one attack and one move.
attack/dex/move/defence die will have sides like this: (work in progress)
Once you roll, and apply rerolls you can spend dice for attacks. You can also save dice, and lock down for the next round - however this means that you won't get to roll them next turn.
It's still a work in progress.