Adding a shadow in Photoshop

I made this shadow from Photoshop by choosing a background and I had to make a boy's shadow like Superman as got a picture of Superman and coloured the entire image black using Shift+Alt+Backspace. I used the Gaussian blur in the filter option to make the black image smooth and lower it's opacity to make it like a shadow. Then, I stuck the shadow and the boy on the wall background and made it like the boy is the next Superman.