You need to provide this data for a correct system installation. The site name will be visible in the system panel, and the client's lists.
Remember to edit the file /includes/sys.config.php with your database settings before installing. If the file doesn't exist, you can create it by renaming the dummy file sys.config.sample.php.
This info will be used to create a default system user, which can't be deleted afterwards. Password should be between 5 and 60 characters long.
After installing the system, you can go to the options page to set your timezone, preferred date display format and thumbnails parameters, besides being able to change the site options provided here.