[Mourn Yauntyyr]

Not sure I understand exatly what you mean.

Do you mean "how do you figure out what 1d10, 1d8 mean regarding damage?" If this is your question, then its simple: the "d" means "dice". Baldur's Gate is adapted from pen and paper Dungeons and Dragons, where you would have to roll dice for damage. There are 4 sided dice, 6 sided, 8 sided, 10 sided, 12 sided, and 20 sided. Also occasionally you'll see 1d3 or 1d2, which aren't dice, but simply mean 1-3 points or 1-2 points. So if you see 2d4, that means "2 rolls of a 4 sided die". That gives you 2-8 points of damage. Similarly, 3d12 means "3 rolls of a 12 sided die", which gives you 3-36 points of damage.

If you mean "how is the given amount of damage assigned to each weapon?" Then that is just how the creators of the game guestimated the effect a weapon would have when used in a nasty manner.

Hopefully that's clearer than mud and I answered your question.

Sreenaur z'hinden,
Mourn Yauntyyr
Elderboy, Qu'ellar Yauntyyr
The City of Tzach Neveril