"The unauthorized use or close imitation of the language and thoughts of another author and the representation of them as one's own original work."
From The Random House Dictionary of the English Language, 2d ed.,
If you copy someone else's words into your paper and you do not give the original author appropriate credit for their work, you are plagiarizing. You are stealing the hard work of another person and passing it off as if it were your own effort.
Research takes time and organization. Start your project early. Take detailed notes that you can refer back to when it is time to write your final paper. If you need help, you can always ask your professor, librarian or campus writing lab for assistance.
You can paraphrase a quote but you still must give credit where credit is due. That means that even if you paraphrase, you must still cite the source in the text right after the paraphrase and add the correct style citation at the end of the paper. (And…changing only a few words does NOT constitute paraphrasing. You really do have to reword the quote and paraphrase in YOUR own words!)