A crontab file has five fields for specifying day, date and time followed by the command to be run at that interval.
* in the value field above means all legal values as in braces for that column. The value column can have a * or a list of elements separated by commas. An element is either a number in the ranges shown above or two numbers in the range separated by a hyphen (meaning an inclusive range).
The specification of days can be made in two fields: month day and weekday. If both are specified in an entry, they are cumulative meaning both of the entries will get executed.
The example below runs the specified command at 23:00 (11:00 PM) every Saturday
* 23 * * 6 (command to run)
The example below runs the specified command at 6:00 and 18:00 (6:00 PM) every weekday (Monday to Friday)
* 6,18 * * 1-5 (command to run)