So, let us begin;
$name = "humbletova"; (you know what this does, right?)
$lengthName = strlen($name); (this puts the length of your $name into $lengthName )
this is where the trick lies and where you obviously got it wrong;
$randm = rand(0,$lengthName); (Now, I see you nodding. Since the total output of the length of your name is inputted into "$lengthName", it means lower 0, higher/total lengthName 9. No additional number needed)
$sString = substr($name, $randm, 1); (In reality, what that means is sString = substr(humbletover, 0-9, 1)). Do you understand? Aww,,,come on! Okay...substr needs a string, start point and the number of characters. What the code above does is, we give the substr function your name as string. random number representing your name and where to start from since rand() anytime it runs outputs a number between 0=h and 9=a and finally, how many character's' should substr output, which is 1.
finally, echo/print $sString;