american english - When do you exactly use a single quote and a double quotes?

He said that the car was "beautifully scratched."
He said that the car was "beautifully scratched".

Where should the full stop be?

1. He said that the car was "pretty."
   


2. He said that the car was 'pretty.'
   


3. He said that the car was "pretty".
   



4. He said that the car was 'pretty'.
   

The difference is in the placement of the full stop and usage of quotes.
Out of these four, which is correct?