Copywhat? Fair who now? Help someone who's never messed with copyright understand it.

I'm trying to make supplements for Vampire The Masquerade with the intent to publish them on Storyteller's Vault. World of Darkness has a licensing agreement called Dark Pact that lets you make, sell and distribute your own content similar to the OGL. However, as someone with no experience ever doing anything that even remotely involves copyright, I'm not sure I know what I'm doing.

I'm writing a supplement focused on minions and followers. It uses a cool new system that expands upon what's available in the core rules. I wanted a cool named, so I called it the Petshop System after Little Shop Of Horrors. I also included a quote from that movie to help the document look better. I'll include the quote below, but regardless...

I'm still not sure if this is okay to do. Or if it could be okay to do. Or if there's a way where it's okay to do. I don't know anything about copyright, and, putting it bluntly, I could really use a crashcourse on this stuff.

Any help is appreciated!

"I'm sorry, Audrey, I'm just so sorry. I never meant to hurt you, I never meant to hurt anyone. It's just that somehow it makes things happen - terrible things. Well, I guess I should've stopped when I found out what it lived on, but it was cute and harmless, and we started doing business and making money and you like me..."