I guess u mean blurring background?
you can achieve blurry background either by setting low f number, shoot AV aperture priority and set ur f number to f.2,8 or lower (if ur lens allows of course). Another way is to zoom in as much as ur lens allows. u will get more blur shooting at 80mm with f/4 then at 17mm with f/4, understand?
fast lens, zoom in all the way is the answer. if this isn't what ur looking for please specify the question. here u go little article explaining
DOF - depth of field