You know to use quotation marks around directly quoted speech or writing. Here are other conventional uses of them:
1. Use quotation marks around titles of movies, songs, short stories, chapter titles with names (not Chapter 10, for example), essays, article names and short poem titles. (You get to decide the cutoff point between short and long poems.)
2. When you use a word in an atypical way, for example: Tomorrow’s test should be a “killer.”
3. Words referred to as words: Every time she says “but,” you know something bad is coming.
Book titles, magazine names, newspapers, operas and plays are conventionally set in italics.