A citation is the basic information that you need to find an article, book, or other resource.
Citations are a form of shorthand -- they look complicated because they cram a lot of information into just a few lines, but once you learn how to read them they begin to make sense.
An article citation will always tell you:
A book citation will tell you:
Some article databases will format citations for you in the cite, save, or email options but be careful -- they are not always accurate.
The Library reference desk has the most recent edition of the MLA Handbook that you are welcome to consult.