Juspeee

Hi, I'm new in Paint.net. I have used a little bit photoshop. I need to create photos like this: http://4.bp.blogspot.com/_0CpRhmNa_ng/TOWXwAEAu0I/AAAAAAAAAHs/nDvDBRy-4QM/s1600/botdf.jpeg So I need to create new background and edit people also so they match with the background. I think i need to remove the original background first, but what do i have to do after that?