Give each submit tag a different name attribute. Then in you PHP script use isset() to check which button was pressed and act accordingly.
test.html
<form method='post' action='test.php'>
<input type='submit' name='button1' value='Button 1'>
<input type='submit ' name='button2' value='Button 2'>
</form>
test.php
<?php
if (isset($_POST['button1']))
{
//execute code for button1
}
elseif (isset($_POST['button2']))
{
//execute code for button2
}
?>