Once we start talking about the actual mechanics of inserting a citation into our text or adding a list of references at the end of our paper, we can't avoid talking about those nit-picky formatting rules you have to use, like APA or MLA. These are referred to as "style guides" and there are hundreds of them. Fortunately, ony a few are widely used. At Illinois Tech, there are only five that are accepted for theses and dissertations: APA, IEEE, MLA, APS, and Chicago/Turabian.
You may be wondering why all these styles exist and why they have such goofy formatting rules. The answer is simple--just think about texting or tweeting. When texting or tweeting, you're trying to convey as much information as possible in as few words or characters as possible. Because of those constraints, people have developed all sorts of abbreviations and shortcuts. In the case of citations, the limitation was in reducing the amount of paper required to print a book or journal. Using a shorthand notation in the main text would never work because there's too much variation, but citations are all very similar, so a shorthand notation for citations is the best way to limit the number of pages printed. A citation includes all the information required to locate a particular source written in as few characters as deemed possible by the publisher. Because different publishers thought different information was essential or of greater or lesser importance, their citation styles differed from one another. In the age of digital publishing, making citations as brief as possible is still vitally important, especially for in-text citations--a long description of a source in the middle of a sentence or paragraph makes reading and understanding nearly impossible. Unfortunately, the wide variety of styles has persisted.
It is not the purpose of this guide to explain the different style guides or how to use them. There are many other sources for this; no need to duplicate them here. Some of the best are: