[Radek]

Unlike your main hand, the efficiency of your off hand depends on your skills. You can attack even without any skill but you need the Shield skill for parrying attacks and the 2nd Weapon skill for getting 2 attacks per round. Without these skills, your off hand isn't more than an inventory slot.
As far as the 2nd Weapon skill is concerned, it is guild level 4 (or 5?) skill. That means Ishad N'Ha. You will need Doublestrike trait (same guild level, same guilds). The 2nd weapon skill becomes efficient at skill level 8 or so.
As far as the Shield skill is concerned, I have no experience. I am always using two weapons.