Ah memories.... Well for one thing, 3.5 is way different from Baldur's Gate as that uses 2nd Ed. rules.
When rolling dice for damage, 1D# means "One #-sided dice", so in your case, a single 10-sided dice. 2D12 would be two dice with 12 sides and so on...
PC-based D&D games really take out the math part of the game for you. Remember clicking on your enemies to attack? Well with BAB (Base Attack Bonus), you add that bonus # plus the stat needed for the attack (Melee is always Strength). The attack roll is basically to see if you hit or miss and if you're lucky, if do critical damage. Roll a 20-sided dice and add whatever number it comes up with to your BAB. Then comes the damage roll, assuming you hit your target. That's when the value of the weapon comes into play. 1D10, 2D6, etc.
Fortitude, Reflex, and Will are mainly used to "Resist poisons/disease, Dodge, and Resist spell effects." These are tied with scores based on character type & level as well as ability modifiers for Constitution, Dexterity & Wisdom, respectively.
Finally Armor Class, or AC, determines if you get hit by an enemy. Unless BG or Icewindale, BIGGER IS BETTER. Thac0 is no longer around since 3.0 Ed. Of course, when purchasing armor, make sure your character class can even wear it and that it doesnt hinder your dex bonus or spell casting (that stuff is listed next to the armors in the PHB I)
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