There are many different versions of the Octobots, but usually, it's a metal ball of varying size with four/eight tentacles controlled mentally by Doctor Octopus via a remote control. They can be used to attack and to perform different tasks. When attached to a person, they can make him/her obey their orders.
It was revealed that a Golden Octobot was used by Doctor Octopus to transfer his brain pattern onto Peter Parker and vice versa, thus enabling Doc Ock to become the Superior Spider-Man.
As the Superior Spider-Man, Doc Ock made robots similar to his Octobots and called them Spider-Bots.