One thing that helped me to understand the elation between aperture and depth of field is the pin hole camera.
The smaller you make the hole the sharper and better the image you get. This is because of an infinite depth of field. But when you make the hole bigger, light rays from one part of the image reaches the screen at more than one single spot and the image becomes blurry. This is a short depth of field.
I may not have been able to fully explain it, but i think i am clear at what i wanted to explain.
This is the site from where i learnt this.
http://digital-photography-school.co...pinhole-camera