In writing, they are used to say, “This part of my paper is exactly what somebody else said or wrote.” Do not use quotation marks when you are paraphrasing what the other person said or wrote.
If what you’re quoting is a long section from another work, and the quote takes up more than three lines of text, do not use quotation marks. Set the quotation off by putting it into an indented block.
For example, if Sam said, “I am going to the store,” you would use quote marks if you wrote: Sam said, “I am going to the store.” However, you would not use quote marks if you wrote: Sam said that he was going to the store, because although that conveys the information that Sam gave you, it is not exactly what he said.
Quoting someone exactly is called a direct quote, and requires quotation marks. Paraphrasing what someone said is called an indirect quote, and requires that you do not use quotation marks. Additionally, indirect quotes nearly always follow the word “that”.
Quotation marks have other uses as well. They must go around titles of short works, such as essays, song titles, magazine articles, and one-act plays, while titles of long works such as books, albums, and movies are italicized.
Quotation marks are commonly used when using a word or letter as itself, rather than using it in its usual context.
The only time quote marks do not come in pairs is when you’re writing dialog and your character is very long-winded. In that case, put opening quote marks at the beginning of his speech, and put new quote marks at the beginning of every paragraph, to show he’s still talking. Don’t use the closing quote marks until he shuts up. If you notice you’re doing this a lot, though, you need to work on your dialog writing skills. Books should not have a lot of monologues in them.