How to read and write cron schedule syntax in Linux

A cron line is five time fields plus a command. The fields are minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-7, where 0 and 7 are both Sunday).

# minute hour day-of-month month day-of-week  command
#   *     *        *        *         *        command

# Every day at 02:30
30 2 * * *  /path/to/backup.sh

# Every 15 minutes
*/15 * * * *  /path/to/check.sh

# Weekdays at 18:00
0 18 * * 1-5  /path/to/report.sh

# Shorthand macros
@daily   /path/to/daily.sh
@reboot  /path/to/at-boot.sh