add function to solr extension

Hi, Can i have some help to create a class to add a function to solr extension ? I want to make a function which send me back the number of results of a query... (field NumFound of array return of SolrResponse::getResponse()) Here is the link to the extension : http://www.php.net/manual/fr/book.solr.php I didn't know how to do. Create or extend a class ? Which one ? How ? Can i have some help to get started please. Thanks by advance. Regards Thomas