The Nestene is a collective or disembodied intelligence which can inhabit and control plastic objects. The Autons are plastic dummies created by Auto Plastics for use by the Nestene Consciousness.
"We are the Nestenes."
"We have been colonising other planets for a thousand million years. Now we have come to colonise Earth."
"Spearhead From Space" (Season 7)
John Ransome designed an electronic doll to be produced by the company Auto Plastics and then headed to America for 6 months to arrange financing. While he was absent, the manager of the company George Hibbert comes under the influence of a glowing globe (called an "Energy Unit") and build an Auton posed as a human called Channing. Production at the factory soon changed to Autons ("Crude weapons with a single defensive function") distributed as manikins across the UK and facsimiles of top civil servants ("perfect reproductions, even down to braincells and memory traces") made for Madame Tassaud's.
More Energy Units fall from the sky, each containing part of the Nestene Consciousness. When all are found and brought together the Autons and facsimiles are activated and the colonisation begins. Fortunately The Doctor finds a way to destroy the tentacled Nestene creature, and thus deactivating the Auton and facsimile army.
"Terror of the Autons" (Season 9)
The Master gets hold of an Energy Unit left over from the previous invasion and takes over a local plastic company to begin mass production of Autons, ugly killer dolls and deadly plastic daffodils. The Master designed the daffodils (which he called Auto-Jets) and arranged for 4,500 of them - which spray plastic to cover the mouth and nose when activated by a radio pulse - across the country so that the Nestene could invade during the confusing caused by the 4,500 deaths.
The Doctor discovers the Master's plan and orders the destruction of the daffodils. Although the Master uses a radio telescope to bring the Nestene to Earth the Doctor convinces him that he too will be one of their victims and the work together to change to polarity of the signal, thereby stopping the Nestene.