So a F-stop of say 20 is "smaller" than a F-stop of 3? 
Correct.
So you zoom around a lot then?
When taking shots where you want the background blurry, yes. The more you are zoomed in, the blurrier the background.
Like in the shots above, you probably do not want the cracked asphalt to be the focus of the image, so use a large f-stop (f4.0) and blur it out. It will bring the focus to your subject faster.
