An APA citation has two parts:
In text (immediately after a paraphrase or a direct quote) - to let the person who's reading your assignment know that this isn't your idea and to give them a quick way to know who's idea it is
Reference list (at the end of your assignment) - to allow the reader to find the article or book that the idea came from. This will give them enough information that they can locate the article or book themselves and find the information that you included in your assignment.
To see how citations look in a paper, check out this sample paper, featured on the APA Style Blog.
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