APA is a citation format commonly found in the social and behavioral sciences. If your research has a humanities bent, such as the exploration of ethics or morals within a piece of technology, it may also be appropriate to use APA for your papers. STEM professors will also sometimes encourage or allow their students to use APA.
This slide deck from the Purdue Online Writing Lab is a good introduction to APA.
Below are examples of APA citations using different source formats.