Ok this might not be the right way, but what I do is:
I take the bit I got, then I cut it
(CTRL + x). Easy enough? Well then you can take the long way, or the short way.
Long: So you've cut it, then it's in your clipboard (but dont worry about that), you take the selection tool and click
CTRL + A. Press delete and everything is gone. Click
CTRL + V and it will be there. All you need to do is drag it to your background.
Short: So you've cut it, then it's in your clipboard (but dont worry about that), you paste it
(CTRL + V) into the background and then move it around.
Sound good?