When citing sources that you find on the Internet you only need to include a retrieval date if the information you viewed is likely to change over time (p. 192). If you reference an article from Wikipedia, for example, you would want to include a retrieval date because information in a wiki can be subject to a lot of change.
In-Text Citation (Paraphrase):
(Author Surname, Year)
In-Text Citation (Quotation):
(Author Surname, Year, page or paragraph number [if available])