How can i use xmlApi

Remember, you will need to have at least reseller access to the server to use the XML-API.

There are some code samples here on the forum. I think one poster even built a PHP class to encapsulate the functionality. You may wish to browse the forums for some of the more interesting discussions that have taken place.

Additionally, there was an entire presentation just on the XML API at last year's cPanel Conference which you can view at: http://www.cpanel.net/docs/seminar07/XML_API.pdf

Of course, there's always the official documentation available at: http://www.cPanel.net/plugins/devel