Example(s)
If you wished to have a script named /root/backup.sh run every day at 3am, my crontab entry would look like as follows:
(a) Install your cronjob:# crontab -e(b)Append following entry:

0 3 * * * /root/backup.sh

Run five minutes after midnight, every day:

5 0 * * * /path/to/commandRun

at 2:15pm on the first of every month:

15 14 1 * * /path/to/commandRun

at 10 pm on weekdays:

0 22 * * 1-5 /path/to/command

Run 23 minutes after midnigbt, 2am, 4am …, everyday:

23 0-23/2 * * * /path/to/commandRun

at 5 after 4 every sunday:

5 4 * * sun /path/to/command