Attack or Offensive stats in Diablo 4 come from your Weapons, Gloves, and Jewelry. They determine how effectively you can deal damage to enemies.
Attack Stats in Diablo 4
Weapon Damage
Skills and passives scale their damage based on your weapon. In the advanced skill tooltip (a setting you need to check in the menu) you can see a percentage next to the damage number. Multiply that percentage by the damage value on your weapon and you get the damage that you deal with that skill. If you have multiple weapons (Rogue or Barbarian Dual-Wielding or Sorcerer with One-Handed Weapon + Focus), add the damage of both weapons together.
Flat Damage
Some effects such as Thorns or procs from certain Legendary Aspects (e.g. Arrow Storms or Trickster's) deal damage that doesn't depend on your weapon. Instead, they just have a flat value that is used as a base for the damage calculation.
Vulnerable Damage
Some skills can make enemies Vulnerable (their Life bar turns purple, or if you are affected, your Health Orb gets cracks). In this state, enemies take 20% more damage from all sources. This 20% bonus can be further increased by your Vulnerable Damage stat. These stats are added together and the baseline 20% before multiplying all your damage.
Critical Strikes
All damage can be divided into direct damage and Damage over Time (Burning, Bleeding, Poisoning). Direct damage happens instantly, while damage over time is spread over a set duration.
Only direct damage can Critically Strike, Damage over Time cannot.
Each hit has a random chance to be a Critical Strike. This chance is equal to your Critical Strike Chance stat, which can be increased in many different ways: You get 5% baseline, 0.02% for each point of Dexterity or Intelligence depending on class, rolls on Gloves and Rings, and many skills and passives.
When you trigger a Critical Strike your damage is increased by your Critical Strike Damage stat, which you can similarly increase: 50% base, rolls on weapons and rings, implicit stat on Swords, etc.
Overpower
On top of Critical Strikes, there's another mechanic that lets you randomly deal more damage. Unlike Critical Strike, chance to Overpower is a fixed 3% chance with no way to increase it. However, some skills have guaranteed Overpower when conditions are met.
Overpower is not a multiplier. Overpower just adds some damage on top of your hit, regardless of how strong this hit was. This damage scales with your Life and Fortified Life, as well as your Overpower Damage stat. Normal Overpower hits are showns in teal, Critical Overpower hits are shown in orange.
Weapon Speed
In Diablo 4, Weapon Speed indicates how often you can cast your skills (although some skills have fixed animation length not dependent on Weapon Speed). Attack Speed can roll as a stat on your Gloves and also comes from different skills and passives.
When dual-wielding, your attack per second is averaged in above caculation.
Attack Power
In your inventory window, you can check your Attack Power which is approximation of your DPS. However it doesn't include a lot of damage bonuses, specifically those that apply only to certain skills or against certain enemies. It also doesn't include any debuffs you can have on monsters such as Vulnerable.
Lucky Hit Chance
In Diablo 4 there's a bunch of random on-hit effects you can trigger with any attack, which are called Lucky Hits. Lucky Hits come from many different sources: skills, passives, items, and Legendary Aspects.
Every skill has a base Lucky Hit Chance, which is something we usually call proc coefficient in other games. This base Lucky Hit chance is multiplied by the chance listed in the Lucky Hit effect.
To view base Lucky Hit Chance on Skills you need to turn on Advanced Tooltips in Settings.
Finally we have a +% Lucky Hit Chance stat that can roll on Rings, Gloves, and Wands (Sorcerer only). All these rolls are added together and they act as another multiplier to your Lucky Hit Chance.
Thorns
Thorns is a special "offensive" stat that lets you deal damage to enemies when they hit you. Damage dealt is increased by a portion of your primary Core Stat. Thorns can roll on Chests, Pants, Shield and you can also boost your Thorns by certain skills and passives.
