installazione drupal su mac

salve,
quando procedo all'installazione di drupal mi esce il seguente messaggio.

The Drupal installer requires that you create a settings file as part of the installation process.
Copy the ./sites/default/default.settings.php file to ./sites/default/settings.php.
Change file permissions so that it is writable by the web server. If you are unsure how to grant file permissions, please consult the on-line handbook.
More details about installing Drupal are available in INSTALL.txt.
The directory sites/default/files does not exist. An automated attempt to create this directory failed, possibly due to a permissions problem. To proceed with the installation, either create the directory and modify its permissions manually, or ensure that the installer has the permissions to create it automatically. For more information, please see INSTALL.txt or the on-line handbook.

come devo procedere?

Grazie