I am using the String library substring() function.
The first thing is I suggest the syntax page be made clearer.
The syntax page should say, the first character is 0 and the last character is length-1.
The first character in the string is position 0 ( the first character in "abcde" is numeric 0)
The last character in the string is length-1 (the last character in "abcde" is numeric 4)
Example
Serial.println("\n\nBegin example showing first and last character in substring");
String sample="abcde";
Serial.print(sample.substring(0,1)); // prints a
Serial.print(sample.substring(4)); // prints e