They can attack just the same as anyone else except they deal lethal damage. They can also grip weapons with that hand, but not with the tool hand.
If you want a rough representation of hand shape, do the vulcan V with your hands with the palm away from you, and put your index finger of the other hand against you thumb, with the lumbs fitting into each other, thats how thick they are. Now turn the hand around and put a finger at the middle of the V and draw it down half an inch, thats how long the fingers are.
For the tool hand, spread your fingers out and do the same half-inch drawing thing.
If I gave them a claw attack it would do 1d3 and still provoke an AoO. And they are humanoids.