QUOTATION MARK ""

Single quotation marks ('') are used only within
double quotation marks ("").

Quotation marks are used to:

 Surround direct speech.
Examples:
She said, "I can't change anything."
He wrote, "She said, 'I can't change anything.'"
Describe special word or expression
Examples: 
Let's call it "candy day"
Let's consider: "o" stands for "no" and "1" stands for "yes"
Mention titles
Example: 
Did you read "The Power with Flowers" book?

NOTE:
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Omit the second question mark outside a quotation 
mark if there is already one inside.
Examples:
He told her, "What did you say?"
Did you say, "What did you say?" she asked him.
All punctuation marks go inside quotation marks
Examples:
He said, "No kidding!"
She said, "Is life an emergency?"