How can I write a lengthy intro paragraph on what fame is...?

Do A LOT of research on Mark Twain, like his biography, the fact that Mark Twain was his pseudonym, authors name only, etc. on the internet and through books, ask a librarian if you're stuck, and use the format given to you. If you need to , take your paper to the Writing Center or teacher/professor for him or her to look at it after you've written your first draft.