um, i wrote a harry potter rap. is there somewhere on here i can post it?

あなた can make it into a YouTube video then emble the exact thing in the box (ex.link) (the last number is fake so don't click on this) or...
If あなた have it on a (safe) website then あなた can put a link to it in the リンク section.

(Interesting, clicking on the link brings あなた to 回答 that need help as well as answered questions..., cool)

あなた can always post it as an article. That's what I would do.