These single quote and double quotes are referred to C/C++ language where single quote is used for single character and the other one is used for multiple characters.
for example:
char sinleChar = 'A';
char multiChar[] = "Hello World";
There's not much differences between them in both VEX and Hscript unless in rare situations where you are dealing with nested strings for instance:
printf("%s", "'Houdini is the best!'");
Which prints:
In this case single quotes are included in the string.
But if you try this:
printf("%s", ""Houdini is the best!"");
Houdini gives you an error!
Hope this helps!