Before we get to the use of quotation marks to show direct quotation, let's look briefly at some special uses of the mark.
Irony or Sarcasm
In speech, you'll often see people use their hands to show that they're putting the word in quotation marks. They are showing a sense of irony:
The police "guarding" the bank slept through the entire robbery.
Use of So-Called
When you use the expression so-called, you do not need to use quotation marks or italics to set off the term referred to. The expression so-called handles the task quite well:
The so-called right to counsel is sometimes ignored in police interrogations.
Referring to Words as Words
When you refer to a word as a word, put it in italics:
When you use the word so-called, you do not need to use quotation marks.
If the word referred to is usually a spoken word, then put it in quotation marks:
Southerners use "y'all" to refer to just about everybody.
If the slang expression is unfamiliar to the reader, enclose it in quotation marks:
When cleaning out his office, the professor hauled away the whole "kit and caboodle."