Every sentence that includes information from a source requires an internal citation. This is true whether you are quoting information word-for-word or whether you are paraphrasing. The only exception to this rule is if the information from a source would be considered common knowledge. Ask yourself, "did I know this before I read it in my source?" or "do most people know this already?"
Save yourself a lot of time and stress - as you take your notes, it's imperative you clearly label which information is from which source.
Just like print sources, online sources are cited within the body of your paper in a way that will allow the reader to find them easily on the Works Cited. Whereas print sources like books require page numbers, online sources do not.
Book Parenthetical Reference: (Atwell 8). – information found on page number 8 in this book written by Nancie Atwell
Atwell, Nancie. The Reading Zone: How to Help Kids Become Skilled, Passionate, Habitual, Critical Readers. New York: Scholastic, 2007. Print.
Online Parenthetical Reference: (Chase). – information found online in this source written by Dawn Chase
Chase, Dawn. "Sustained Silent Reading in the High-School English Class." California English Dec. 2000: 16-18. Education Research Complete. Web. 22 Nov. 2011.
When there is no author: (“Global Publics”) or (Stanford Copyright). -- Use what comes first in the Works Cited entry, usually the title or an abbreviation of it:
"Global Publics Embrace Social Networking." Pew Global Attitudes Project. Pew Research Center, 2010. Global Issues In Context. Web. 12 Feb. 2014.
Stanford Copyright & Fair Use - Copyright and Fair Use Overview and Resources.Stanford University Libraries, 2007. Web. 12 Feb. 2014.
NOTE: punctuate the abbreviated title within the citation the same way as in the Works Cited entry.
Are you concerned you may have accidentally plagiarized? While not foolproof, here are some free plagiarism checkers that can help you check.