I got an example...I got a picture with a white background,

I want to put this background to replace the white background :

This is ONLY an example , i want to put one of my picture with white background and put anoter picture background on it. Thank you.
~ Vincent
P.S : My english is poor

I don't really understand the tutorial someone showed me because i dont have the same version or something , could anyone just tell me where to click and all :S