But I don't quite understand this fan club.. can someone tell me what I need to do?
I agree with Sydian, but I think you're maybe asking what RNG abusing is? RNG abusing is abusing the random number generation in the Pokemon games to manipulate the Pokemon you receive to get what you want. When I say manipulate it's more like precise timing and understanding of simple programs to determine what seed pops up at different times.
If you already understand that then throw what I just said out of the window. This club's main purpose is for people who enjoy RNG abusing Pokemon to gather and share our recent RNG abuses, ask questions about RNG abusing if we're having issues, and complete little challenges that the owner of the club comes up with.
I'm a newbie here so don't take my word for it but I believe I'm right. Also the guide here by TwilightBlade is a lot better than Smogon's. Prettier pictures :3