Group notes are visible to everyone and can be used to track upcoming events to pray for.  Maybe a group member has a job interview.  Maybe it's a friend or family member who is ill.  You can add to these notes by clicking on the calendar icon in the top right corner of your home screen and clicking Welcome.  

Private notes might be where you want to record how a particular message is speaking into your life right now.  At the bottom of your daily scripture, questions and study notes you will see the Private notes tab - click this to start a note. These are only visible to you.

If you want to see all your group messages and Private notes in one place, simply click the Group Details button which is the second icon along from the left, at the bottom of your screen (appears as a circle with three dots) and click 'Notes.'

If you require any further assistance with this particular issue please raise a ticket here to speak to a customer support agent. Here is a video walking you through the process: