A citation style (or format) specifies what information should appear in your citation, how that information is ordered and how it is formatted (punctuation, italics, etc.). APA, MLA, Chicago, Vancouver and CSE are examples of citations styles.
To know which citation style to use, consult with your professor. If your professor doesn’t have a preferred citation style, APA is normally recommended as it is well documented. CSE is a citation style that is preferred in the field of biology.