Ideas, facts, or passages of text that you found in a source all need to be cited.
You can either
Paraphrase an idea or fact by putting it in your own words,
or
Quote a source by using the author's exact words in your paper.
Either way you must give credit to the source you found the idea in!
If you mention the author's name you need only cite the page number in parenthesis. For example:
He writes that fascination with the night sky is a universal human reaction. (Sagan 34)
Sagan suggests that fascination with the night sky is a universal human reaction. (34)
When you quote a source you need to include a name and a page number.
For example:
"Even today, the most jaded city dweller can be unexpectedly moved by a clear night studded with thousands of stars." (Sagan 34)
If you include the name of the author in your sentence you can leave the author's name out of the parenthesis.
For longer quotes, you need to do a block quote. You do not need to use quotation marks in a block quote, but you do need to indent the entire quote. Here is an example.
Sagan writes that
Sometimes a work does not have page numbers. In this case, you often do not need a parenthetical citation at all, so long as you work the author's name, or title of the source if the author is unknown, into your paper.
This is the best way to cite websites, films, presentations, or personal interviews. Use your judgement; you need to include enough information for your reader to find your source in your works cited list.
A few examples:
George Lucas' Star Wars combined a science fiction premise with a clearly drawn battle between good and evil. While the story is as old as fiction, and the script often leaves something to be desired, the film's influence and hold over the popular imagination is undeniable.
According to Brant and Henkelmen's website Achemenet, the Persian Empire controlled much of the modern Middle East during its heyday.
In both cases the writer references the work and gives their reader enough information to find it in their works cited page.