Hello there, in thsi post im gonna explain how to place an image of yours to another background with few easy steps..
follow the screen shots and try it out
1 open your image that u want to modify and take the magnetic lasso tool from the tool box
select your image using that tool
go to edit and select copy and then again go to edit and select paste
note that your selected image will be separated as a separate layer
open the background image that you want to use and go to select menu->select then to edit->copy
paste the new image in the document that you already separated your image
note that the new image you pasted will be on top of the separated image and the old background image.
use the mouse drag the new image layer and put it under the separated image layer
and this must be your result.