STRING*  MyFunction()
{
   STRING* tmp_string = str_create("hello");
   return(tmp_string);
}

OR

STRING*  MyFunction()
{
   return(str_create("hello"));
}

and call it with

function main()
{
   ...
   STRING* Returned_string;
   ...
   Returned_string = MyFunction();
   ...
   //remember you will need to use
   str_remove(Returned_string);
   //when youve finished with it.
}

STRING* tmpStr = str_create("#10"); //creates a string that contains 10 spaces
str_trunc(tmpStr,1); //cut the last space and we can fill this position with a character
str_cat(tmpStr,"X"); //lets put an X on the end of the string
//lets print the string
printf("This is what the \"tmpStr\" contains:\n%s",_chr(tmpStr));

...
STRING* temp_string = MyFunction();
str_cpy(Existing_String, temp_string);
str_remove(temp_string);
...