APA in-text citation is a method used to acknowledge and cite sources within the text of a research paper or academic document. It involves putting brief references within the body of the text to indicate where specific information or ideas have been sourced from. 

In general, you should use a citation any time you use someone else's words, ideas, data, or information in your work.

One complete reference for each in-text cited source should appear in the References page at the end of the paper.

What not to cite:

It is best practice to cite whenever possible.  However, there is no need to cite:

• Common knowledge. Common knowledge includes facts that are found in many sources. In general, if a fact can be found in five credible sources, a citation is not necessary. For example, you would not need to cite that the Declaration of Independence was signed in 1776, or that water is comprised of hydrogen and oxygen.
• Generally accepted or observable facts. When a fact is generally accepted or easily observable, you do not need a citation. For example, “smoking may be bad for your health” or “most people use cell phones” are both generally accepted and easily observable. Be careful, however; if you venture into more specific knowledge, you should cite a source. For example, if you want to provide specific numbers of teenagers that text while driving or the incidence of lung cancer among smokers, these require citations.
• Original ideas and lived experiences. When writing about yourself or your lived experiences, a citation is not necessary. Original ideas, including the write-up of results from your own research or projects, do not require citations.

Adapted from Boston University.

In APA style, the basic format for in-text citations typically includes the author's last name and the publication year of the source, enclosed in parentheses.  If you are directly quoting an author, you should also include "p." or "pp." and the page number or numbers.

Here are a few examples of different scenarios:

1. When directly quoting a source:
   According to Smith (2020), "quoted text goes here" (p. 45).
    
2. When paraphrasing or summarizing a source:
   Heavy social media use can be linked to depression and other mental disorders in teens (Asmelash, 2019).
    
3. When citing a source with multiple authors:
   (Smith, Johnson, & Davis, 2021), or Smith et al. (2021).
    
4. When citing a source with no identifiable author:
   ("Title of Article," 2022), or (Title of Book, 2022).

The format of the author element of the in-text citation changes depending on the number of authors and is abbreviated in some cases.

• For a work with one or two authors, include the author name(s) in every citation.
• For a work with three or more authors, include the name of only the first author plus “et al.” in every citation (even the first citation).

The following table shows the basic in-text citation styles: