ty for ur all answer guys. I got it some

but some

divinitty 2 was better , I havent understood yet

I will try to summarize for you.
If your weapon's damage is 2d6, it can do 2 to 12 damage at random. double on critical hits: 4-24.
This damage is added to your attribute modifier used to attack (usually: strength or dexterity, depends on the weapon and its properties), your modifier is ([attribute-10]/2), if your attribute is 18, your modifier is 4. So your damage is 2-12 + 4.
But if the weapon has + enchantments, then add that + to the damage granted. If it's +1, then your damage it's 2-12+4+1.
Going back to modifiers, every 2 attribute points, increase the modifier or decrease it by 1, the zero point is 10.
8 is -1
10 is 0
12 is 1
18 is 4
20 is 5