In order to add your tasks and subtasks in Doneit as events to your calendars, please firstly tap on the task’s or subtask’s title in the list or create a new task or subtask. On the 'New/ Edit' screen, please tap on the 'Reminder' option, then make sure that the toggle for the 'Add to Calendars' option is turned on, you can then select the calendars that you would like to add this task or a subtask to.