Here is how Multiweapon fighting and natural attacks work
Characters have Primary and Secondary natural attacks
Primary Natural attacks use the full attack bonus (Bite, Claw, Gore, Slam, Sting, and Talons are primary)
Secondary Attacks use the attack bonus -5 (-2 with multiattack)
If you use a weapon all primary natural attacks are considered secondary and take that penalty. Natural attacks do not interfere with weapon use, but obviously if your using a weapon in your left hand, you cannot use your left claw.
If you have three or more arms you can wield more then one weapon. One of those weapons is considered your Primary weapon and the rest off hand. Now the rules don't outright state how this works (annoyingly but there are no races or classes that allow you to have extra arms by default...) but there are two safe interpretations
1) If all your off handed weapons are light then offset the multiweapon fighting penalty by 2
and
2) Off hand weapons take 2 less penalty for being wielded. If all your off hand weapons are light your primary weapon also gets 2 less penalty. (My personal ruling)
Note that you can wield two handed weapons if you have multiple arms as normal. So if you have four arms you can wield two, two handed weapons.
Now there is only ONE difference between Multiweapon Fighting and Two Weapon fighting... Multiweapon fighting isn't used as a prerequisite for any feats. So there is no "improved" or "Greater" version of it.
Though to attack more than once still requires a full attack (though there are some feats and abilities that allow you to do otherwise)
So lets put this all together
A Minotaur with six limbs, horns (gore specifically), six slams (one for each hand), and say 2 tentacles... wields four daggers and attacks with a total attack bonus of 6+/1+
We are going to assume he has multiweapon fighting and multiattack
So first of all since he is using an weapon his gore and slams are considered to be secondary taking a -2 penalty. He can only use two slams because his other arms are taken up by the dagger (I hope I am right and Slam isn't a full body attack). Tentacles are already secondary attacks so they stay the same. He has a light weapon in all his off hands that are wielding weapons so his penalty is -2 in the primary and -2 in the offhand.
He attacks with his primary hand is 4 and -1, Multiweapon attacks are three 4 attacks, gore at 4, two slams at 4, and 2 tentacles at a 4.