straight and curly quotes
Always use curly quotes
Straight quotes are the two generic vertical quotation marks located near the return key: the straight single quote ' and the straight double quote ".
Curly quotes are the quotation marks used in good typography. There are four curly quote characters: the opening single quote
Straight quotes are a typewriter habit. In traditional printing, all quotation marks were curly. But typewriter character sets were limited by mechanical constraints and physical space. By replacing the curly opening and closing quotes with ambidextrous straight quotes, two slots became available for other characters.
Word processors are not limited in this way. You can always get curly quotes. Compared to straight quotes, curly quotes are more legible on the page and match the other characters better. Therefore, straight quotes should never, ever appear in your documents.