I couldn’t think of a better place to learn how to cite an html source, or specifically, a URL, than to go to the Wikipedia.

the Wikipedia page on Citing Sources [in HTML] is quite useful– but take care to notice that they are also indicating specifically how to cite sources using the Wikipedia software, known as MediaWiki. Nevertheless, the information needed to learn how to cite sources inline in an HTML composition (such as in a Blog or a Community Forum, or Newsgroup) is there in abundance.