Log in to the server via the ssh.
Let's say you would like to set a cron for a user "test"
"crontab -u test -e"
and you'll be able to write a cronjob.
If this is the first time you creat a cronjob, you will be editing
a new file.
Enter something like
"* * * * * command.sh"
and save the file.
#The first part of the cronjob means the freqency.
For example, "* * * * *" means every minutes. The command will be executed every minutes.
"9 3 1 * * command.sh" means the command is done
at 3:09 on the first day of the month.
"0 12 * * 0 command.sh" means the command is done
at 12:00, every sunday.
#You can check the current cronjob by typing
#The result will be sent to you by email.
If you don't need it, you can write the cron like this.