The field for tags is mt_keywords, as reference see this ticket.
The field for the category is categories.
Important is it, that you have a array for the fields, like
$categories[0] = "cat1";
$categories[1] = "cat2";
$tags[0] = "tag1";
$tags[1] = "tag2";
$content[ 'categories' ] = $categories;
$content[ 'mt_keywords' ] = $tags;
As reference for each field it is better you use the source, not the online plattform. You should find it all in the class wp_xmlrpc_server.