Any Pathfinder adventuring party is likely to have a small arsenal of weapons and dangerous magic at their disposal. They better for beating the snot out of all the creatures, cutthroats, and cultists they're sure to fight. But not every attack does the same kind of damage—after all, a sword hurts differently than a splash of acid to the face.
Plus, many monsters a party will encounter will have resistances to certain kinds of damage. It adds variety to combat encounters and forces players to work out a strategy for taking down highly resistant enemies. It also makes the fantasy world you're exploring feel more real and consistent. Because it wouldn't make sense to kill a fire elemental with a fireball.
10 Physical Damage
Physical damage types are the most common. They cover bludgeoning, piercing, and slashing damage, which are generally the kinds of damage a party's weapons—swords, spears, maces, etc.—will deal. Bludgeoning comes from blunt force trauma, like being clubbed with a warhammer or falling from a great height.
Piercing is stab or puncture wounds, caused by arrows, spike traps, or a beast's fangs. Slashing is being cut open, like from the swing of a sword or axe. Many incorporeal monsters, like ghosts, will be heavily resistant to nonmagical physical damage, and will sometimes have some resistance to even enchanted weapons.
9 Elemental Damage
Elemental damage caused by players is most often delivered through the use of offensive spells, but can also be caused by the environment. The kinds of damage covered by this are acid, cold, electricity, fire, and sonic damage.
Most of these are self-explanatory. Fire burns, acid dissolves, and a shock of electricity can shut down your nervous system. Cold can also kill by freezing solid, or just the slow running down of being caught in a blizzard. Even sufficiently loud sounds can hurt if used correctly. Elemental damage is a great way to overcome a monster's resistance to physical damage types.
8 Positive & Negative Damage
Positive and negative energy work a little differently than the more straightforward elemental damage types. Positive energy, often from a divine source, is most often used to heal the living, closing their wounds and giving them back their strength.
But it's so at odds with the negative energy that infuses the undead that casting a healing spell will cause them to wither and weaken, dealing positive damage. Conversely, the negative necromantic energy that gives the undead power will sap a living beings strength, dealing negative damage while at the same time revitalizing the undead.
7 Force Damage
While this could be considered a kind of elemental damage, it works a little differently than the other more natural elements. Force damage is caused by an exceptionally pure and powerful magical effect. Like if the weave of mystical energy that permeates the world made a fist and punched you with it.
Very few creatures have resistance to force damage, even incorporeal creatures like ghosts, making spells that cause it a powerful tool in a spellcaster's arsenal.
6 Alignment Damage
If you have a weapon or spell that deals a certain kind of alignment damage, it's kind of like playing Rock Paper Scissors with whatever you're fighting. Alignment damage comes in four flavors: lawful, chaotic, good, and evil. Whatever kind of damage you're dealing will only affect creatures that have opposing alignments, because the damage is antithetical to their nature.
So if you have a blessed blade that deals good damage, only evil creatures will be affected, or a spell that deals chaotic damage will only harm lawful creatures.
5 Mental Damage
Some effects specifically target the mind of a creature. Depending on the spell, it can twist the target's mind with enough force to actually cause harm. Whether it's a cosmic mind break caused by forces beyond comprehension or just insulting a baddie so precisely that they drop dead, the mental damage it causes can be just as fatal as a stab wound.
However, not all enemies will be vulnerable to mental damage. Creatures with particularly rudimentary intelligence just won't have enough of a mind to rend. And constructs, like golems or robots, whose actions are programmed by someone else, probably won't be affected either.
4 Poison Damage
Poison damage can be caused by many different vectors. The player characters might have eaten something entirely inadvisable and made themselves sick. Or they might be fighting a monster with venomous barbs designed to paralyze them. Or maybe they just brushed up against a patch of evil poison ivy.
Poison damage will often be recurring due to long term afflictions, which will have their own special negative effects for you players. But the damage itself is distinct from other kinds of physical or elemental damage.
3 Bleed Damage
Bleed damage is similar in some ways to poison damage. It's usually a secondary effect caused by some other physical attack. What sets it apart from whatever slash or puncture wound that actually injured the character is that bleed damage is persistent.
It will continue to drain health and strength from the injured creature for a period of time without its enemy having to make any further attack rolls. This can make it especially dangerous for party members, or very valuable to them during a difficult boss encounter. Just make sure you have a healer in the party.
2 Nonlethal Damage
Nonlethal damage works differently from pretty much every other form of damage. Essentially, reducing an enemy's HP to 0 using nonlethal damage knocks them out instead of killing them. Certain weapons have the nonlethal property, which makes them deal nonlethal damage by default. Making a lethal attack with a nonlethal weapon incurs a penalty.
However, you can choose to make a nonlethal attack with a weapon normally used for lethal strikes, in case you want to keep one of those goblins for later. It does incur the same kind of penalty though, so be aware.
1 Precision Damage
Precision damage is another kind of specialized physical damage. The flavor is usually that, through precise movement and knowledge of your enemy's weaknesses, you can cause extra damage with a well-place strike. If, for example, rogue's sneak attack deals 1d6 precision damage, they are striking at a vulnerable part of their foe with their dagger.
Precision damage does the same kind of damage as the attack that triggered it, so in this example the target would receive an extra 1d6 piercing damage from the dagger for precision. There are a few enemies that are immune to precision damage entirely, usually creatures like oozes with undifferentiated anatomy.