Dual wielding in this system is very simple. If you're using a 1-handed weapon in each hand, you make an attack with each one every turn. Normally, the main-hand roll will be at +1 DC and the off-hand roll will be at +3 DC. However, if you have the Ambidextrous perk, each roll is only made at +1 DC. The same applies to non-combat things such as writing with both hands at once.