All sources mentioned in the paper must appear on the reference page. When using APA format, your in-text citation should follow the author-year model, for example (Smith, 2012). The author-year model always appears at the end of the sentence in parentheses. If you cite the author within the sentence, you only need to include the publication year of the source.
According to Purdue OWL,
Students often had difficulty using APA Style, especially when it is their
first time citing sources. This difficulty could be attributed to the fact that many students
failed to purchase a style manual or to ask their teacher for help. (199)