TL;DR
Personal activities can live alongside schoolwork. Mark a task private when it should not appear to people viewing your planner.
Before you begin
Create or edit a task you own; you cannot rewrite the teacher's original assignment.
Key points
Add the activity with a clear title and date.
Use a personal class or the suitable class option available in your planner.
Enable the task's privacy setting for sensitive personal details.
Check privacy before sharing: connected parents and teachers do not see private tasks.
Related help