Step 4: Reduce Hit Points

Any remaining damage reduces the target's Hit Points on a 1-to-1 basis. More information can be found in the Hit Points, Healing, and Dying sections.

Nonlethal Attacks

Source Player Core pg. 399

You can make a nonlethal attack to knock someone out instead of killing them (see Knocked Out and Dying). Weapons with the nonlethal trait (including fists) do this automatically. You take a –2 circumstance penalty to the attack roll when you make a nonlethal attack using a weapon or unarmed attack that doesn't have the nonlethal trait, or when making a lethal attack using a nonlethal weapon. Spells and other effects with the nonlethal trait that reduce a creature to 0 Hit Points knock the creature out instead of killing them.