I want to know this because I saw that @EnPassantFork made today's one, and I would like to have a crack!
You can't, only staff can.
You can create your own puzzles: https://support.chess.com/en/articles/8639952-how-do-i-put-a-game-or-puzzle-in-a-forum-post
I want to know this because I saw that @EnPassantFork made today's one, and I would like to have a crack!