The Autons are humanoid robots made of living plastic and being made of plastic, they resemble mannequins in stores. They move slowly, almost never speak, and can't grasp anything.
Since they are made of living plastic, it doesn't matter if their body is broken up. If an Auton loses its arm or leg or head, the parts still move.
The reason they can't hold anything is because their hands are guns. When activated, their fingers will flip down and a gun barrel will point out, shooting flashes of light.
A karate chop from their arms can also cut through metal. An Auton can also shape itself to have weapons. When the Auton of Mickey Smith was fond out, it shaped its hands into blocks in an attempt to attack the Doctor.
Autons can also duplicate people. Unlike the Dalek Duplicates that download a persons thoughts into them, Autons shape themselves to resemble the person. However, in this case, the Auton must keep the real person alive or the Auton copy will die.