No, not quite. I'm not at a PC right now, so this is a very paraphrased version.
If you are dual-wielding you get one extra attack per round if you have attacked twice in the round. You have to declare this at the start of your round and make your three attacks, and you get -2d6 to all of them.
You have to use AGI as your attack attribute; not STR (melee) or INT (ranged).
If you have the Ambidexterity trait, the -2d6 goes away.
You can dual wield with any weapons you can hold in one hand, ranged or melee. Makes no difference. Rapier and pistol is actually a fighting style I used with a musketeer, and it's pretty cool.
You can't generally use unarmed attacks as a dual-wield unless you have some kind of exploit or something that says otherwise.
Alternatively, your off-hand weapon can be used for defense if it has the Shield trait, as long as you do not attack with it. You get a flat DEFENSE bonus in that case. Shields are normally used in this way, but can be used to attack as a dual-wield, losing their DEFENSE bonus.