Piece of cake!
1) Create a new document properly sized to accomodate both pieces of art (you can check Image Size under Image to verify the sizes of the art you're working from-make sure the canvas is white!)
2) With your new document and the documents for the 2 pieces of art open, drag the background art into your new document using the Move tool (just click anywhere on the art on drag it into the new window)
3) If necessary, use the Move tool to position the background art properly.
4) You can "fade" the background back by adjusting the Opacity level in the Layers palette.
5) The next step is a bit trickier. To add the figure, you'll want to drag it and it alone into the new document (just dragging the whole piece of art in will also bring in the white background). In this case, selecting the figure is pretty simple. Just use the Magic Wand (I'd set the tolerance level to 20 or so) and click on the white background (shift + click if you need to add isolated parts of the background to the selection-underneath the arm for example).
6) Once you have the background selected, go to the Select menu and click Inverse, that will give you a selection containing just the character.
7) Using the Move tool, click and drag the selected figure into the new document, position properly-and voila!
Looking at this artwork, making the Magic Wand selection should be fairly simple. As you work on more complex subjects, you'll need to spend more time on making your selections. There are many excellent tutorials out there for using the other selection and masking tools available to you. This is a nice one to start with though to get good practice.
Good luck!
