How works on examples mb_stripos:

First we will watch example on symbols(..?).
<?php
$text = "Look! It's a text! Wow!"; //simple text
$spaceIsHere = mb_stripos($text," "); //you can replace " " on something what you need or want
$text2 = mb_substr($text,$spaceIsHere); //cutting text with $spaceIsHere
print ($text2); 
/* Print will show that result:
" It's a text! Wow!"
Look. That " " wasn't cutted, because mb_substr don't write in var position after " " - he write WHERE is " " in string. */
?>

Also it can work on words, sentences...
Here's one of examples:
<?php
$text = "Look! It's a text! Wow!"; //familiar text, right?)
$afterNeededWord = mb_stripos($text,"text!"); //you can replace "text!" on something else what you need
$text3 = mb_substr($text, $afterNeededWord); //cutting string (it is string? im stupid in that question xD)
print ($text3); 
/* Print will show that result:
"text! Wow!"
Explaining the same. */
?>

I hope it was useful with my "good" English skills. ;D
Have a nice day, coder.