Example
// filter by creation date
$date = new Zend_Date();
$toDate = $date->get(Zend_Date::W3C); // today
$fromDate = $date->sub('1', Zend_Date::MONTH)->get(Zend_Date::W3C); // one month ago
$orders->addAttributeToFilter('created_at', array('from' => $fromDate, 'to' => $toDate));
// more filtering, type AND
$orders->addAttributeToFilter('status', 'pending');
$orders->addAttributeToFilter('state', array('nlike' => 'new'));
// more filtering, type OR
$processing = array('eq' => 'processing');
$complete = array('like' => 'complete');
$orders->addAttributeToFilter('status', array($processing, $complete));
