The purpose of this guide is to teach you about resistances, dealing damage and receiving damage, along with things that can increase or decrease damage taken outside of resistances. Please note that damage can be resisted via a lot of sources and your mathed out damage will NOT always be the same as your actual output.
All damage in the game has a type. There are three standard melee damage types (slashing, bludgeoning, piercing) and two nonstandards (silver and cold iron).
The “damage bonus” you can get off of items is a direct bonus to all melee damage that stacks with your attribute modifier and the item's enchantment level. A direct bonus does not effect the damage dice, instead adding it to your base minimum (keep in mind many weapon types, I.E. dagger versus longsword, will have different damage ranges). If I deal 1d8 silver damage with my unenchanted silver sword and have +2 damage bonus, my true damage range is 1d8+2, thus a minimum of 3 and a maximum of 10.
Enchantment bonus directly adds to attack and damage bonus behind the scenes, so if I enchanted my silver longsword to +2, that would make my damage 1d8+4 (min of 5, max of 12). Your relevant attribute modifier (strength for all melee weapons unless using Weapon Finesse, dexterity for all ranged weapons) adds a hidden and direct damage bonus as well as to-hit bonus. This means, if my modifier for strength was +1, I'd have 1d8+5 in the same formula.
Critical hits are exclusive to weapon and unarmed combat and multiply the damage you'd have done with that roll by your weapon/fists' critical multiplier (this means Monks can easily crit for 300+ later on with their bare hands). The only exception is the Magus' Spellstrike which uses your modified critical range and doubles spell damage done during Spell Combat. Spell Combat itself reduces ALL spell damage done, however, so this more equalizes it with a similar level caster. Some feats can add to your critical range and your critical multiplier. Your critical range is how often you will proc it, it's the range of what you have to roll to get a critical hit. (16-20 is much better than 19-20, because you can critical with 16 roll and up instead of just a 19 or 20 roll). Critical hits from weapons also get a bonus damage roll based on weapon type, this can be as low as the same damage range (i.e. a 1d6 staff with a 1d6 critical bonus damage roll) or much higher in the case of certain weapons (pistols, daggers).
Lastly, there are some abilities and feats that will give you niche damage/attack bonuses. Favored Enemy and Bane are two of these and will not show their damage or attack bonus unless in combat with an applicable target.
Steps to formulate your weapon damage: 1. check weapon type ('discern weapon'), save damage range 2. do 'bonuses' and get your damage bonus number 3. check your relevant stat modifier (the number in brackets under 'stats') 4. check your weapon's basic enchantment (the + or - if it has one) 5. add numbers from steps 2, 3 and 4 to create one sum 6. add niche bonuses i.e. bane, favored enemy to this sum 7. add damage range of weapon + this sum Your result should end up something like 1d8+30 (if you have 10 modifier, a +10 weapon and +10 damage bonus). This meaning you deal 31 to 38 damage per normal hit if you succeed on your attack roll. To calculate base critical damage, multiply the minimum, I.E. 31, by your weapon's critical multiplier. If your damage is always returning low or as 1s, you do not have the proficiency feat required for the weapon. Without the proficieny required, your damage output is divided by 100.
Pugilist Monks: 1. see your class helpfile/wiki page and get your damage range+critical damage multiplier 2. do 'bonuses' and get your damage bonus number 3. check your relevant stat modifier (only if using weapon finesse) 4. check your fist enchantment level (based on class formula+if you have Enchanted Fists) 5. add numbers from steps 2, 3 and 4 to create one sum 6. add niche bonuses i.e. bane, favored enemy to this sum (this includes Unchained feat and similar) Your result will end up, at level 40 Monk/10 GrMaster with +10 modifier and without feats, 2d10+20 Your critical damage multiplier will be 7 at this stage, too.
Spell damage comes in very many types, but relies on a couple of extra things. Saving throws, when passed against your spells, will either halve or remove the damage done entirely (based on relevant feats being present on the target; Stalwart, Evasion). A very small number of spells do not have saving throw checks, but they tend to be rare, single target and have no status effects added on. Spell damage is calculated, additionally, in a more complicated way than weapon damage. Standard damage rules apply your caster level and the level of the spell (I.E. level 9 for Typhoon) to most spells that do damage (travel AoEs such as Vampiric Shadow Shield, Fire Shield, Wreath of Blades do not use spell level, instead they use a standardized formula that will always be lower than actively cast spells).
Magic resistance/spell resistance is a method to completely prevent spells from effecting you at all and some mobs, as well as players built for it, have fairly high amounts. Likewise, spell damage resistance and elemental resistance, whether percentile or static, will factor into how much damage you can do with spell damage resistance applying to all spells regardless of element. Spell reflection is another way a target can get out of taking damage from you, but it locks them into casting the spell and this means they cannot stack an attack feat ontop of it or, in most cases, get their round of melee attacks.
To be completed.