To create a cron job as root, edit your cron file:
[sudo] crontab -e
Add a new line at the end, every line is a cron job:
25 10 * * * php /var/www//artisan
This will execute the same command at 10:25AM everyday.
Just make sure you keep a blank line after the last one. And you also might need to use the full path of your php client:
25 10 * * * /usr/local/bin/php /var/www//artisan
