Edit/list crontab:

# optional: –u {username}
crontab –e
crontab -l

A cron job follows this syntax:

minute hour day(month) month day(week)    command/script

You can do things like this:

# At 00:00 on day-of-month 1 and 15 and on Wednesday
0 0 1,15 * 3    some_script.sh

# At 22:00 on every day-of-week from Monday through Friday
0 22 * * 1-5    some_script.sh

A neat website is the crontab guru¹ which provided the above examples.