When filming movies, you can blur the background by adjusting aperture or using a long lens. One easy method is to choose aperture-priority auto exposure mode and adjust aperture as desired, leaving the camera to set exposure. Choose low f-numbers to soften backgrounds.
To soften backgrounds, you'll need to pay attention to two factors. One is to use a lens with a long focal length: the longer the lens, the more shallow the depth of field and the softer the background. The second is to choose a lens with a wide maximum aperture: the wider the aperture, the more shallow the depth of field and the softer the background. Note, however, that a shallow depth of field makes focus challenging, rendering these techniques unsuitable for filming moving objects. Adjust depth of field to suit your subject.
To adjust aperture, choose mode P, S, or A. Keep the exposure compensation button pressed and rotate the main command dial to choose a setting. Choose lower f-numbers to decrease depth of field, higher f-numbers to increase depth of field.