Welcome to the QuickBooks Community forum, andrew1234. I'd be glad to show you how the reminders work in QBO.
The reminders created in QBO won't automatically get sent out. Instead, you'd have to manually send them whenever a transaction is due.
On the other hand, the Recurring Transactions feature is not available in the Simple Start version. You might want to upgrade to the Essentials or Plus version to be able to use this feature.
Please let me know if you need more help.