Linux Crontab Format to Schedule Cron job

Crontab is used to schedule scripts, applications and backup to run at given time.

Crontab file fields 

Crontab has 6 fields(first 5 for specifying time and 6th one for executing scripts or command etc.)
The first five fields are separated by either a space or a tab and represent the following units, respectively:

* Minutes {0-59}

* Hour {0-23}

* Day of the month {1-31}

* Month of the year {1-12}

* Day of the week {0-6, 0=Sunday}

crontab Options 

#crontab -e --to edit or configure

#crontab -l -- to list all jobes

#crontab -r -- to remove job  

I will take one example here to explain crontab,suppose I want to execute one script located in /test/script.sh and save the output to /tmp/script.out should be executed every 15th of each month at 11:56pm

#crontab -e   

56 23 15 * * /test/script.sh > /tmp/script.out

here * in month field and week field indicates any month and any week execute this script