When creating or editing a ToDo, tap "Advanced" to set a "Due" date and a "Notification".
- When you set a "Due" date, the ToDo is shown on the calendar on that date (you can show or hide the mark on the calendar with "Calendar Settings" → "Show ToDo Marks" in the settings screen)
- When you set a "Notification", a reminder arrives at the date and time you set. If it doesn't arrive, check in your device's "Settings" app that Smart Planner's notifications ("Todo reminders") are allowed