The start date is the date after which jobs will be automatically created and scheduled under the Recurring Job's settings.
Example 1
If you set a job to recur on the first Monday of October every year, with a start date of 31 October of the same year, the start date (31 October 2022 in this example) is after the recurrence date (first Monday of October) in this calendar year, so the first job won't be created until next year for the first Monday of October 2023.
Example 2
If you set a job to recur on the first Monday of November every year, with a start date of 1 November of the same year, the start date (1 November 2022 in this example) is before the recurrence date (first Monday of November) in this calendar year, so the first job will be created this year for the first Monday of November 2022.