Ethylene is also called Ethene. It's chemical formula is CH₂=CH₂.
It is made when natural gas is "cracked" by heating under pressure.

Chlorine (the green atom) is added to the ethylene to produce Vinyl Chloride Monomer (VCM).
CH₂CHCl

The VCM can then be polymerised. Many VCM molecules are joined together in a long chain to form PolyVinyl Chloride, or PVC.

The PVC can then be modified and moulded into many applications. To make flexible PVC, plasticisers are added.