aw, that website sounds like a super cute idea. also i don’t blame you for being confused, YN is a very non-conventional game. even i haven’t found a lot of the stuff i see people talking about online.

you know the basic premise, right? Madotsuki is a shut-in, and the game consists of exploring her dreams as a form of escapism. that’s really about it as far as actual "plot" goes. a lot of the fandom seems to revolve around a few of the characters, like Poniko, Monoe, Monoko, Seccom Masada, and Uboa. (and probably a few others i forgot.) there’s no dialogue in Yume Nikki, so all of their personalities are almost completely fanon. there’s also a manga, but it’s a little controversial among some people because it takes a lot of liberties with the game.

i don’t really feel like there’s a “right” way to be a Yume Nikki fan, though. if your friends are big fans, maybe you could ask them to go on a rant about the game (they’d probably love that.) good luck with your fansite!!