What is the Difference between ". . ." and '. . .'?

Double quotes and single quotes seem to be used interchangeably. Is there a difference, and should I use one over the other or both at different times?

Thanks.

Not much! Just better to use one or the other.

https://www.codecademy.com/forum_questions/53e513f18c1cccff95000075
https://stackoverflow.com/questions/944081/what-is-the-difference-between-and-in-javascript

Thanks!