Green screen is used in editing to put any background you want behind the main actor or actors. This is used for backgrounds that you can't find naturally for example in star wars they needed a lava planet so they green screened it in.
You get the actors to film the scene like they would but they would stand in front of a green screen, then in editing they would play around and add a background either a moving image or just a picture.
4 films that use green screen is, star wars, James bond, The avengers, man of steel.
Props we will need is an horse mask.
