Well, it depends on what type of combat you want.
Assuming that you're doing Twine you will probably choose to do turn-based combat.
Turn-based combat is actually very simple.
The first step is to enter a "Combat Loop"
Every Turn goes a little like this.
1. Check if you or your enemy is dead.
2. You/Enemy have a turn, that deals damage/Lust/ Whatever you desire.
3. Swap, so its the Enemys/Your Turn.
If you keep at it, you will have a never-ending loop of actions between Player, Enemy.
Once you reach 0 hp you want to navigate to a Passage "You Lost" and if you won you want to go "You won" Passage.
