The Green screen inable the making of the film and/or t.v. show to add effect or to put a characters in a place that they have and can’t film at.

i.g. Star Wars: In the attack of the Clone (second movie), Obi-Wan is flying in his Jedi fighter and being shott at by Jango Fett in space, everytime they have the scene shot on Obi-Wan inside the fighter, everything in the fighter is being really filmed and everything outside the fighter is just add in because everything outside is all green scene, the space part of the scene is add by cutting out all the green from the background.

In this day in age they’re not many films that don’t use green screen in there movies and as long as we make movie there will always be green screen to make films 

Every movie and T.V. show go by this step, they can’t work without it 

source:
Episode Engine