APA (American Psychological Association) is a citation style commonly used in some, or most, social sciences. The current edition of APA is the 7th edition. Please check with your professor to determine the correct edition of APA that is being used for your assignment(s).
Here are two general examples of citing sources using the APA citation style 7th edition. For further detailed help, please refer to the APA Style Manual and/or the "APA Help" box.
Print book
Heimberg, R., Turk, C., & Mennin, D. (2004). Generalized anxiety disorder : Advances in research and practice. Guilford Press.
Journal article (found in a database)
Pop-Jordanova, N. (2019). Different Clinical Expression of Anxiety Disorders in Children and Adolescents: Assessment and Treatment. Prilozi, 40(1), 5–40. https://doi.org/10.2478/prilozi-2019-0001
The APA citation style is used mainly in the social and behavioral sciences, natural sciences, nursing, communications, education, business, engineering, and other fields. Check with your professor to see which edition you should use as both editions are being used.
Publication Manual of the American Psychological Association by 
Publication Manual of the American Psychological Association by