APA is a citation style designed by the American Psychological Association. This style supports the study of psychology and many social sciences including business research. The style book called Publication Manual of the American Psychological Association contains all the style rules. The APA puts up some of the common formats online for free. The library also has print copies of this manual but I believe for this class teh APA will have most of the examples you need such as journal, magazine, book, website.

Citation in class work is important to help distinguish between your ideas and the ideas of others.
It depends! There are multiple organizations which have their own format such as the Modern Language Association (MLA), the American Psychological Association (APA), and The University of Chicago Press.
Your professor will indicate what style they want you to use. Usually they will pick a style they are familiar with so they can easily determine what sources you have used in your paper. First check you syllabus and then if it is not in your syllabus ask your professor.
Many academic article databases will have an option to generate a citation. Keep in mind automated citations are sometimes not correct so you will need to double check what is generated. But they do usually give you most of the information you need to make a citation.
There are also tools on the web which offer to generate citations and the quality varies.
I recommend ZoteroBib. But keep in mind it may be wrong so double check the quality.
If you use a citation generator your and it provides a badly formatted citation, your professor can still take points off. You are responsible for correct formatting so use the authoritative resources from APA or MLA or Chicago to double check the quality.