1. Create a new note
You can find the icon of notes at the upper right corner of the scene's main page. Press the note icon and a notepad will pop up, where you can write down your personal thoughts.
Every tool also has a note icon at the upper right side of the page. So you can also write a note to an event (attendance), to a folder, to a task, etc.
2. Editing notes
In the notepad, you can find the ordinary formatting opportunities. Don't forget to click "Save" after you've finished editing your note.