Kit lenses are ' slow ' ..in other words, they start with larger F numbers ( f4 / f5 etc ) which means less DOF ( depth of field ) which is how much of your subject and background is in focus. With a kit lens, you can still get a blurry background, but you just have to make sure the background is further away from your subject. The further away YOU are from your subject, the further away they need to be from the background. Using the the smallest F number on your camera, and standing as close to your subject as possible, ( before lens refuses to focus ) combined with a background that is some distance away, will give you the best blur possible.
Having said that, there are caveats with using your lowest F number. Sometimes kit lenses are soft at that aperture. You'll just have to experiment to see what you can get away with. If you have to go to a larger number, say from f4 to f5.6, you will get slightly less blurry background, but possibly a sharper subject. Again, experiment. If using f5.6 instead of f4 and you find the blurry background is not enough, either get a bit closer to your subject, or if that isnt possible because you were already as close as you can get before the lens will no longer focus, then you need to move your subject to where the background is further away
