Having trouble in Drupal setup

warning: dl(): Unable to load dynamic library '/usr/lib/php/extensions/xml.so' - /usr/lib/php/extensions/xml.so: cannot open shared object file: No such file or directory in /var/www/html/includes/xmlrpc.inc on line 40. warning: Cannot modify header information - headers already sent by (output started at /var/www/html/includes/common.inc:384) in /var/www/html/includes/common.inc on line 99. warning: array_map(): The first argument, 'utf8_encode', should be either NULL or a valid callback in /var/www/html/includes/common.inc on line 1775.