Exaplin !, @ and % with Examples?

!variable, which indicates that the text should be inserted as-is. This is useful for inserting variables into things like e-mail.
<?php
    $message = t("If you don't want to receive such e-mails, you can change your settings at !url.", array('!url' => l(t('My account'), "user/$account->uid"))); 
?>

@variable, which indicates that the text should be run through check_plain, to escape HTML characters. Use this for any output that's displayed within a Drupal page.

<?php
    $title = t("@name's blog", array('@name' => $account->name));
?>

%variable, which indicates that the string should be HTML escaped and highlighted with theme_placeholder() which shows up by default as emphasized.

<?php
    $message = t('%name-from sent %name-to an e-mail.', array('%name-from' => $user->name, '%name-to' => $account->name));
?>