APA states that you should "cite the work of those individuals whose ideas, theories or research have directly influenced your work" (APA, 2010).
APA guidelines require citing sources within the text [or body] of the paper using an author-date citation system. Every resource cited in the text of your paper must be listed alphabetically in the reference list. Likewise every resource in the reference list must be cited in text with the exception of classical works such as the Bible and personal communications you've had. These are not listed in the reference list.
SUMMARIZING OR PARPHRASING:
Format: APA style requires specific kinds of information be included in in-text citations. The author's last name and the work's date of publication must always appear & are all that is necessary when citing an idea, an entire book, article or other work. Example: (Smith, 2009). These must match exactly the corresponding entry in the references list. The page number appears only if it is a direct quotation. Example: (Smith, 2009, p. 195). Placement of the cite may vary within the body of your paper; There are several options of where to place the citation in text.
Groups as Authors: When the author is a group (e.g. association, corporation, government entity etc.) their name is generally spelled out each time it appears in a text citation. If the group's name is long and there is a well known abbreviation use it in subsequent in text citations. Examples: 1st time: (Mothers Against Drunk Driving, 2009); Subsequent uses: (MADD, 2009).
No Author: Use the first few words of the reference (usually the title) and the date. Use double quotations marks around the title of an article, a chapter or web page and italize the title of a journal, book or report. Examples: ("Comparing learning styles," 2009) OR (Learning the Alphabet, 2009).
Indirect Sources: When you use a source cited in another source, name the original source in the narrative. The secondary source [the one you used] should be listed in your reference list and cited in parentheses. Example: Roberts study of children found .... (as cited in Smith, 2009).
Electronic Sources: Generally electronic sources cited within the text should be treated the same as print sources by including the author's name (or brief title if there is no author) and date in parentheses.
Short Quotations: If you directly quote from a source and the quotation is 40 or fewer words include it in the text and enclose it with double quotation marks. There are several ways to handle this depending upon where in the sentence the quotation appears. Generally the source is cited in parentheses immediately after the quotation marks and includes the author's name, date and page number including 'p.'. Examples: (Smith, 2009, p. 195) OR Smith (2009) found that "children's learning included ..." (p. 78).
Long Quotations: When you quote directly from the source and the quotation is more than 40 words display it in a free standing block without quotations. Quotation block should appear on a new line indented at least 5 spaces from the left margin and be double-spaced.
Online Sources: Credit online sources using the authors' name, date and page numbers in the same manner as print sources. If there are no page numbers but paragraphs are visibly numbered use them in place of page numbers. Use the ¶ symbol, or the abbreviation "para." in place of the page number. Examples: (Smith, 2009, ¶ 3) OR (Smith, 2009, para. 3).
If the paragraphs are not numbered but there are headings within the document or page list the appropriate heading and indicate the paragraph number under that heading. Include the author's name, date, heading title and indicate the paragraph under the heading.
Purdue University Online Writing Lab (OWL). (2010). APA style. Retrieved from http://owl.english.purdue.edu/owl/resource/560/01/