Blur or Bokeh
One topic that photographers and videographers always are interested in is how the blur the background of their shots while maintaining focus on the subject.
Aperture
Aperture is a key term we need we need to be clear on. Aperture is simply the opening inside the lens that allows light in. It can be closed and opened. It is often related in what is called the f value. Its a little counterintuitive, but the bigger the f value the smaller the opening and the smaller the f value the larger the opening.
The smaller the f value on a lens, the easier it is to get some nice blur. Usually lens with a large aperture (small f value) are more expensive as a rule simply because they have to be bigger (wider).
The Blur Equation.
Don't worry there is no math involved lol. This is just one simple way of putting together a shot to maximize the blur. Basically Min distance to subject + max distance from subject to background + max aperture = Max blur of background.
Even if you don't have a large aperture lens, you can still get some blur by implementing the rule above.
Its Not Rocket Science LOL
But it is physics, but not too hard to remember. Here is a video I did that will show you what I mean better than typing it.