APA Style is from the American Psychological Association. It is a very widely used style in the social sciences--not just in psychology. It is probably the most commonly used style on campus.
APA 7th EDITION
In 2019, APA released their new 7th edition of the APA Manual. Many of the changes make your life as a student easier! Although everyone should be using this new edition now, it would be smart to double-check with your professor whether they want you to use this edition. You should also make sure that any online citation tools you use are based on the new edition.
Get started with this summary of what's new: APA Manual 7th Edition: The Most Notable Changes.