Key Frame

First of all think of an idea and select a photo or video to use then record on the green screen.

Once this is done and youve uploaded it to final cut pro then it time to select them and put them on top of one another, once this is done select the chromo key tool and then it time to use the paint tool and select all the green part getting rid of them. This will then leave you with you and the video or picture of your choice. Simply render and you are done. 

https://www.youtube.com/watch?v=6Rdey9xfr9w