[john70t]

Those can lights look to be in series. One switch to control them all.

Why is the f'kin neutral/white not connected?
(Those push connectors and much of the modern hardware sucks, fwiw. Use the screws properly.)

Black=hot.

White=neutral or return.
These can sometimes be crossed up and back-feed on the same circuit. Be warned.

Green=ground to pipes and/or grounding rod.
A good safety feature and never to be ignored when zipping things up.
When the fixture frame is 120V energized from a short, you touch the fixture while standing in water on an aluminum ladder, the juice is supposed to bypass and jump to ground instead of through your body.