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.
For this class, you will use the Conservation Biology Citation Style. The journal is using APA 7th with one major exception - "do not include DOI when volume and page numbers or e-page numbers are provided". If you are using EndNote or Zotero, select APA 7th and write your paper. When you're done, go over your references. If it includes volume/page numbers/e-page numbers, remove the DOI.