Here is an example of an in-text citation in an author-date style:
In their review of the literature (Knapik et al., 2015) some themes emerge …
This style uses an approach in which an author-date are located / identified directly within the text when a source is used, which then allows the reader to find the full reference to the source at the end of the essay on a separate references list (or bibliography).
Here is an example of an in-text citation in a numeric style:
In their review of the literature (1) some themes emerge …
This style uses a numbering system, where an alpha-numeric figure identifies that a source has been used/referenced. The reader can then locate the full reference in the reference list at the end of the essay.
Here is an example of an in-text citation in a notes and bibliography style:
In their review of the literature1 some themes emerge …
This style uses footnotes or endnotes, where the full details of the source are given in the footnote (at the bottom of the current page), or in the endnotes (at the end of the essay). If the same reference occurs again an abbreviated form is used in the footnote/endnote. All references also appear in full on a separate references list (or bibliography) at the end of the essay.