Ok, not “all” but maybe 50%
There are lots of ways of controlling it… some are able to be done IN the camera with the lens, but some cameras like smartphones don't always do that.
But here's a sample of what i'm talking about that is done IN the camera.
same subject, but the background on the left is so freaking distracting and on the right, you're eye sees nothing but what the photographer wants you to see.
And no i'm not trying to say you HAVE to buy a dslr to do it.
I'm trying to get you to think about the background in every shot and how it will impact what you're shooting.
Sometimes you can totally change the image by changing the angle — like shooting from below — or by moving around.
This image is something I shot at the Missouri Botanical Garden. It is the SAME branch of a flowering bush that was sticking out of a trellis. I wish I had taken a wider shot to give you a better idea of the space.
I simply walked around it and watched the changes of the background.
The first frame (Bright green background) was on the left of the branch, the second was looking back at the trellis, and the remaining 3 were all shot on the right side looking back toward the left.
Remember it is about telling a story.
If the viewer is distracted, your story isn't as effective.
So now are you thinking about what is behind your subject?