Dual wield is the ability to use 2 weapons instead of just one. Only the Barbarian and Fighter are able to dual wield. These Classes require the talent "Dual Wield" to be learned before you are able to equip 2 weapons.
There are many benefits to dual wielding. The major benefits are: The ability to do 2 attacks per round, and the chance to have weapon abilities land twice. For example, the has the ability to land 2 critical hits in a single round.
Drawbacks may include lower defense for your Fighters due to the lack of shields.Off-hand weapon damage is lowered to 50% + 15% with Dual Wield Specialization.
To dual wield two handed weapons, learn the skills "Strength of Giants and "Dual Wield." You can reset your skills after obtaining the ability and duel wielding two weapons to keep on duel wielding, though you lose the ability as soon as you remove the offhand weapon. You can save skills points this way. Works for "Strength of Giants" as well.