$ crontab -e       (edit)
*  *  *  *  * date >> ~/out.txt
man 5 crontab
crontab -l         (list)

User specific file:

/var/spool/cron/crontabs/USERNAME

System-wide crontab files:

/etc/cron.d/
/etc/cron.daily/
/etc/cron.hourly/
/etc/cron.monthly/
/etc/crontab
/etc/cron.weekly/