When a PC tries something risky, call for a saving throw. They must roll a d20 equal or under the relevant ability score to pass.
Attacking automatically reduces the target’s hp by the damage listed next to the attacker’s weapon. When no hp remain, any further damage directly reduces str and the victim must pass a str save or suffer critical damage. They are out of action and will die in an hour unless tended to.
Armor reduces damage by the defender’s listed armor score.
If circumstances warrant, you may declare an attack to be impaired (d4 damage) or enhanced (d12 damage).
If a PC’s str is reduced to 0 they are dead. If Wil or dex drops to 0 they are out of action.
A short rest of just a few minutes restores hp. A week-long full rest somewhere safe restores ability scores and heals other serious ailments.
Using Wreck (magic items and technology) in an unusual way requires a Wil save to avoid a mishap.