This is not something that can be described in a forum post in sufficient detail.
I recommend that you find a person who knows how both light and shoot for Chroma Key, which is also known as Blue Screen or Green Screen. You will need to plan out your shooting very carefully, and you will need the help of someone who has done it before.
If you choose to do it on your own, you can expect to take many weeks of study, shooting, practice, failure and re-shooting.
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA