Thac0 stands for = To Hit Armor Class 0. so if you're Thac0 is 10, and someone has an armor class of 3, you would roll 1d20 (one 20-sided di) and need a 7 or over to hit the opponent. the game does this for each attack your player makes.
As far as damage goes, each weapon has a base amount of damage it can do. Some of these are:
2handed sword = 1d10 (meaning a 10-sided di is rolled and causes that amount of damage)
long sword = 1d8
staff = 1d6
dagger = 1d4
these are just a few. extra damage can be added if the weapon is magical, like a staff + 4, which would do 1d6 + 4 added on to the roll. a character can gain greater damage capabilities with mastery specialization in a weapon, or magical items like girdle of hill giant strength.
the computer also generates this number each time you character makes an attack.
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trux
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