I am far from an expert on this camera but as nobody else has answered, I'll have a go.
One of the main reasons you may not have received a reply is that I don't think the DSC-WX500 has the 'background defocus' feature. I know the DSC-WX50 had it but not the WX500.
All background defocus does is to open the lens aperture wide open to give the minimum depth of field. Basically, this does not work very well at all for cameras with a small sensor so, you probably don't have the right camera to exploit this noticeably as you may see it on a SLR camera.
The best way is to put your camera into 'A' mode - aperture priority mode - and manually open the camera to the lowest f-stop available and take the picture. This is also similar to Portrait Mode (which the WX500 does have) that does the same thing with a few skin tone tweaks.
I don't think background defocus is available in movie mode but if you are looking to film something like racing cars, the camera should be able to follow-focus a moving car and blur the background as long as you are panning the camera with the car.
Can you please check exactly which camera you have and describe how you have set it up for background blur. Also let us know what you are trying to capture.
