When you turn on calendar integration, tasks are registered as events or reminders. Only tasks with both start date and due date are registered as events. If you integrate with Reminders app, tasks without start date and due date are also registered.
You can integrate with the Calendar and Reminders by turning on "Integrate with Calendars" in the app's "Settings" > "Calendar Integration". If you are using multiple devices, enable calendar integration only on the device you use most frequently, as it can cause duplicate events.
Tap or click the URL in the notes field of the registered event or reminder to go to FirstSeed Tasks and open the edit screen for the corresponding task.
At the bottom of the notes of registered events and reminders, there are IDs and other information to link them to tasks. Note that if you edit this section, the integration will not work correctly.
If you turn on "Sync Start & Due Dates" in the "Settings" > "Calendar Integration" in the app, changes made to the date and time of events or reminders from external apps will be synced to tasks.