Answer:
If you're asking how you managed to do that, it sounds like a lens problem (smudges, dirt or defect). It can be done with a special soft focus filter, or you can modify a skylight or UV filter by smearing a bit of vaseline on it. Note that you view the scene at maximum aperture, so you will not be able to preview the result unless you can stop down the lens to the aperture you will use before taking the shot. Alternatively, I think your only other recourse is image editing software. I can't recommend one...don't use.