Proper Use of Quotation Marks
Only use quotation marks when something is being quoted. Don't use quotation marks for emphasis.
Quotation marks can be appropriate even when someone is not being directly quoted. Suppose Bob has a new girlfriend, but he says they are just friends. You might write something like this:
Remember to invite Bob and his "friend," Susan.
The word "friend" is more or less a quotation from Bob. The use of quotation marks implies that you don't really believe him.