Animal skin is turned into leather via number of quite complicated steps.
First the majority of animals are killed for the meat, so the skin is of secondary importance. To stop it putrefying, ie falling apart, the skin must be preserved. This is done by adding common salt to the skin and piling them on a pallet. The salt kills the bacteria involved in the putrefying process. Once preserved, the skin is taken to a tannery where the hair and any remaining flesh have to be removed.