Green Screens are an interesting technology, used for all kinds of interesting effects. The first Star Wars Movie was done with green screen techniques, however computers make it a whole lot easier today.
Step 1: Hunter/Gatherer
Fold as shown.
Step 5: Change the Background
Start by cropping down to just the screen and object.
Remove the green using a magic wand or colour selection tool.
Replace with cool new backdrop of your choice.