how to extract the letters in php code example

Example 1: take 10 character from string using php

$return_string = substr("Hi i am returning first 10 characters.", 0, 10);
Output:
"Hi i am re"

Example 2: only display part of string php

substr('abcdef', 1);     // bcdef
substr('abcdef', 1, 3);  // bcd
substr('abcdef', 0, 8);  // abcdef
substr('abcdef', -1, 1); // f