What is FEP for?

What is the FEP transparency sheet for? Do I put it somewhere on my halot mage printer? I am trying to print directly on my VAT so I do not know what to do with the FEP.

There is not any clear instructions what I am supposed to do with it.

The FEP film is installed the vat of the 3d printer and needs to be replaced from time to time due to wear and tear.