If you are in a class or any of the following subjects are your major, you will most likely use the APA format:
6th edition APA formatting
7th edition APA formatting
DOI stands for Digital Object Identifier. It is a persistent, unique number that identifies a piece of online or digital information, such as a journal article, a chapter in an online book, a data set, a map, and so on. Students most often encounter DOIs when they're citing journal articles. Keep in mind that not every journal article will have a DOI assigned to it! Look for the DOI on the first page of the article, either at the top or bottom. You need to include them in your citation as they are very helpful when trying to locate the article later.