Q. How do you know if you need a citation

When you cite a source you do so in two places:

1) In text where you use the source.  At the end of your sentence put (Author's last name, Year of publication).

2) At the end of you document, you create a References list.  Each source you use is listed there alphabetically in full.  

To know how exactly to cite for each place, you start with the type of "source" you are using.  Then you can use an APA style guide for instructions.  A source is the type of material (ex. book, newspaper, journal article or magazine, website, etc.).

Here are some links with some additional guidance:

In-text: https://owl.purdue.edu/owl/research_and_citation/apa_style/apa_formatting_and_style_guide/in_text_citations_the_basics.html

Reference list: https://owl.purdue.edu/owl/research_and_citation/apa_style/apa_formatting_and_style_guide/reference_list_basic_rules.html