Once you adopt the fanfiction idea, you can do whatever you like with it and you can post it wherever you like. If you like a story idea, please leave a review for that chapter saying you'd like to adopt it. When I see a story has been adopted, I will delete that chapter so others know it's been adopted and to make room for other story ideas.
The fanfiction story ideas I currently have up for adoption are Phineas and Ferb stories (thus why I'm posting in this fandom), but more fandoms will be added. When more fandoms are added, the category of this story will either change to Misc or the appropriate fandom.
Happy adopting!