Settings : Preferences (App Icon Badge, Notifications, Time Zone, etc.)
App Icon Badge
You can pick a list for App Icon Badge. On that list, all the overdue tasks will be shown on App Icon Badge. If you check 'Undated Tasks', it'll be added to the number. Also number of tasks without time that's set for today will be added if 'Today - No Time' is checked.
To use notifications in GoodTask, you need to turn it on. Be sure to turn off notifications for Reminders app to not get duplicate notifications. To turn off notifications for Reminders.app, go into 'Settings.app > Notification Center' and turn it off for Reminders.
You can select sounds and choose snooze time that can be used by swiping the notification.
Start Week on
You can select weekday to start week on. This will be used on week view and month view.
Next 7 Days
If you turn this on, week view will start from today to next 7 days. Above 'Start Week on' option will be ignored on week view.
If you choose a time zone, it'll be overrided to all your tasks. Even if you travel to somewhere that have different time, time on tasks will not be changed if it's set.
This is same as 'Sort Options' that can be set on additional actions at Tasks page.
You can upload your preferences to iCloud and use it on other devices. Also you can import from GoodTask 2 if it's installed on same device. When you install GoodTask 3 on new device, pop-up will show up if you have saved preferences.