For edit: crontab -e
For view: crontab -l
# minute hour(24) dayOfMonth Month dayOfWeek(0-6, 0=Sunday) command
To schedule my server to chmod 644 the access log,
0 10 * * 0 chmod 644 /var/log/apache2/access.log
Task will perform every Sunday at 10:00 am.
Thanks to http://www.crontabrocks.org/