Before you begin work on any research paper, examine the assignment closely for any requirements.
Q. How long is the paper?
This could be a page length, a page range, a word count, etc.
Q. How many sources?
How many total sources does your instructor ask for; are they all outside sources or does your textbook count as one of your sources?
Q. What kind of sources?
Does your instructor specify certain types of sources? Are there other requirements such as how current/old the sources can be, or where the source should come from - the library, a database, a book/ebook, etc.?