Ask your instructor if he requires you to use the URL for online sources. The 7th edition does not require you to list the source's URL unless it is needed to find the page, but your instructor might still want to know the URL to double-check your sources.
Cite online sources at the end of your paper using the basic format:
Author's last Name, First Name. "Web Page Title." Organization/Publisher. Website Name, Publish Date. Web. Access Date. Italicize the name of the organization or replace with "n.p." if the page does not have a publisher. Replace the date with "n.d" if the page does not have a publish date. Omit other parts of the citation if the Web page does not have them.
Format in-text citations using only the author's last name and page number -- do not make up a page number if one does not exist on the Web pages. Use an abbreviated version of the title in quotes if the Web page does not have a specific author. Examples include "(Author)" and "("Main Page Title")."