Base attack

 

There is two different base attack bonuses, Melee and range. Each has it's set of bonuses like magic, skill, size mod, race and others.

If you have one than one attack, each attack bonus will be separated by a slash.  

Some Advanced Skill management may fill in the "skill" box bonus. The races screen may also fill in the "race" bonus box for ranged and melee attacks.

The Right and mod and Left hand mod are not automated. You must the enter the penalties in those boxes if your character uses two weapons.

You can select what weapon each hand will hold, and the google to the right of the selection combo box will get you to the Character Gear update screen. The weapons listed in the box are those that your character has in it's equipment. If you want a new weapon to appear there, you need to add it to your character.

The number of attacks for a class is defined in the Class level update screen.