this command submits, edits, lists or removes cron jobs. 

to edit the crontab entry

to list all scheduled job of a particular user

remove cronntab entries

it run the myscript.sh everyday at 8pm

it runs the myscript.sh yearly

it runs two scripts daily 6am

run the specified task at the sysstem reboot

we can see the current looged in user

-i option with -r is used to get the y/n response before removing the crontab