Why do you need to cite sources?
Check out what the MLA Handbook has to say:
"Every time you write a research paper, you enter into a community of writers and scholars. ... MLA style represents a consensus among teachers, scholars, and librarians in the fields of language and literature on the conventions for documenting research, and those conventions will help you organize your research paper coherently. By using MLA style, you will direct your readers to the sources you consulted in arriving at your findings, and you will enable them to build on your work." (MLA xiii)
You will also want to avoid plagiarism, which is a very serious offense involving the theft of intellectual property. In college, and elsewhere in the professional world this can result in serious personal sanction, and potentially even lawsuits. 'Plagiarism' is derived from the Latin word plagiarius- meaning 'kidnapper' (MLA 52). It means stealing someone else's words and representing them as your own. Generally speaking, this applies to the written word. Quoting an author, or paraphrasing what someone else has written is actually fine, provided you cite them correctly. Check out the 'citation help' box (to the right) for resources on how to cite books, websites, and articles. Make sure you are properly citing sources in your papers.