Attached Link: Background

If you are going by the tutorial, the author has already provided the background.

All you have to do is open that picture in photoshop along with the picture of your figure.  Then just do the drag and drop the background layer onto the figure layer.  Of course, you need to resize or crop one of the image as necessary to fit together, although you could just render the figure image in same size as the background.

OTOH, if you are creating your own, then you would need to do two renders.  One for the figure only and one for the background only.  Export each render from poser as TIFF, and open them in Photoshop and follow the above step.

Let me know if you got this far.