Notes are pieces of information you can log for reference on a People Record. They are best used for recording observations about a patron or organization, their preferences, or bits of prospect research.
This section of a People Record is free-form. It houses whatever details you deem relevant to doing business with this person that don't fit into action. Basically, notes can be used to document anything from general patron housekeeping to fun facts about that person that will help you make your next conversation with that person a little bit more personal.
If you click on a note, and then click on the Edit button, you'll see more details about which user created the note and when.
You can also star important notes. Only the first three starred notes will show up on the top of a People Record, but the rest will appear when you click the "X more notes" link.