Plagiarism and references

Reading the chapter over plagiarism has gotten me to wonder how many times I may have plagiarized when I was in school years ago. I was never taught to list references when I was in school and if I was, I do not remember it. We was just given a topic and sent to the library to write. So when I started here at Kaplan it took me a while to get used to references and citing. I am still a little worried that I may mess up on listing the reference wrong or something like that. I do see the importance in citing our sources; to give credit to the person who wrote it. The thing I am still confused on is why different types of sources such as journals, books, etc. have to be cited differently on the reference page. You think that just citing them one way would be okay, but I guess not. I mean, I don't mind doing it I was just curious as to why they are different is all :)