If you were telling someone that they absolutely had to read this awesome article you found: what kind of information would you give them? But you also sometimes need to know more in order to help someone find it. You might share what page you found something on, when it was posted, or even give a link to the article.
Controlled Chaos
With all the possibilities, it's best to have a set of directions on what information to include and in what order. These rules help people who know how to "read" a citation to know what they are looking at without you having to say "The author is ____. The title is _____."
So how do you know what to do? You follow the directions.