The input: three nouns.
The output: whatever you can imagine.
"Take Three Nouns and Write" is exactly what it sounds like: you get three random nouns to write into a piece however you please. Work them in sequentially, spin some scenario to connect them, or simply juxtapose them in your mind and see what they inspire.
This flexible prompt lends itself well to both poetry and flash fiction, though you could no doubt also get inspired for nonfiction with it. Fans of longer forms can give themselves regular infusions of threes (one per page? per hour? per chapter?) or just double down on their original triad. As I said, your imagination's the limit.
(At least one other version of this prompt exists, but I wore out their generator from overuse, so I figured I'd put my own set of nouns up here.)
What are you waiting for?