As the name indicates, these notes are personal and can only be seen by you.
When in a meeting room in Arthur, click on the yellow notes icon 
floating on the bottom of your view.
Your private notebook will open, where you can take personal notes during your meeting.
Take notes using the keyboard
You can take notes using the keyboard for text input. You can move the keyboard to your most convenient location and you can also resize it using scaling.
Take notes using a pen
By clicking on the pen icon 
on the top right of the notebook, you can switch to taking notes using a pen. Pressing the menu button will open the draw settings to change color, erase or choose a different pen thickness.
You can switch between the pen and the keyboard by clicking on the respective icons ( 
) on the top right of the notes.
Continue to:
How do I export my personal notes?
Do my notes stay in my personal notebook after leaving a VR meeting?