If it is a flat image duplicate the layer and delete the "Background" layer you can then delete selections to make it transparent.
If the edges are well defined around the subject in the photo make sure that the Magic Wands "Contiguous" box is checked and adjust the tolerance... that is the amount of levels it selects that are different from the source point so that it selects most of what you want. If it makes a good solid selection you might want to click "Refine Edge..." and feather it a bit. You may want to try the "Quick Selection" tool as well.
After you get it selected you can just hit delete and it will remove the selected stuff you can then go back over it with the "History Brush" and paint back in the parts you want to keep but removed.
Note: There are million ways to accomplish what you want that is the great thing about Photoshop this is just one of them.