Use quotation marks

for direct speech

Janet asked, "Why can't we go today?"

For quotes inside quotes, use single quotation marks.
Billy said, "So then John told her 'I don't want to go today' and Janet cried."

for words that are defined, that follow certain phrases or that have special meaning

1) Stating a definition.
'Buch' is German for book.

2) Following phrases such as entitled, marked and the term.
The book was signed 'Terry Pratchett'.

3) Special meanings, noting inaccuracies or misnomers, etc.
The 'free gift' actually cost us forty pounds.