For citing in the text use the author-date format, for example:
According to Smith (1999) ....
it has been proven ... (Smith, 1999)
Author, A. A. (Year). Title: Subtitle. Location: Publisher.
Malcolm, J. (1980). Psychoanalysis: The impossible profession. New York, NY: Vintage Books.
Surname, A. A., Surname, B. B., & Surname, C. C. (Year). Title. Periodical, volume number(issue number), pages. DOI
Coudounaris, D. N., & Sthapit, E. (2017). Antecedents of memorable tourism experience related to behavioral intentions. Psychology & Marketing, 34(12), 1084-1093. https://doi.org/10.1002/mar.21048
Online documents can take various forms; here is an example of a webpage:
Surname, A. A., & Surname, B. B. (Publication date). Title of webpage. Title of website. URL
The World Bank Group. (2018). What we do. The World Bank. https://www.worldbank.org/en/what-we-do
To check out how to cite other online information sources, visit the Purdue OWL Electronic Sources section
A primary source can take various forms; it could be an image, a video or manuscript. For each form you need to follow different rules in order to cite it. Check out Purdue OWL Non-Print Sources to find out more.