PCBs, copper pours, ground planes, and you

Ok I'm gonna ask a potentially stupid question as someone who knows little to nothing about electronics. The article (and every other source I looked at when trying to answer my question) points out the blank spots on the board as a copper pour. Where, exactly, is the copper? I just see green plastic. Is it on the back side and nobody is taking photos of it?

The green is solder mask. It's just a coating that goes over most of the board, to prevent oxidation and accidental electrical shorts and to prevent solder from sticking where it isn't supposed to at the assembly stage. (You can get solder mask in different colors as well. The board itself is usually actually a sort of yellowish white and made of FR4, a kind of fire-resistant fiberglass.)

Generally you can sort of see through the soldermask to see the copper traces underneath. In the example images in the article, the lighter areas are copper and the darker areas are the space in-between.

> to prevent ... accidental electrical shorts

It frequently does that, so you are not wrong, but it is not a reliable insulator. If you need insulation or spacing for engineering or compliance reasons, you cannot rely on solder mask to provide it.

I mean the kind of shorts where you accidentally drop a screw on the PCB, drag a loose wire across it, or something like that. Not foolproof, but it probably reduces the risk of damage somewhat.