These are just "Notices", not "Errors" or "Warnings". They don't impact the running of your script and are displaying because you've got your error_reporting level set unnecessarily high in your php.ini file.

See here for more details:
http://us2.php.net/error_reporting

You can change the Error Reporting setting in your Joomla>>Global Configuration>>Server page or change the setting in your php.ini file according to the link above.

Thanks!