Navigate to a pupil's profile either by searching for them in the search bar (top right corner of the page) or by clicking on their name on an open page.
Once there, simply go to the Edit tab and scroll to the bottom of the page. There is a limit to how much you can type in here; however, it is millions of characters so this should be sufficient for your note. Press Save to save your changes.
If you want to write more detailed notes or upload/attach documents to a pupil's profile, see 'How to manage documents'.
To add a note to one of the pupil's contacts, simply click on the contact's name and again scroll down to the Notes section.
You can easily see which pupils or parents have notes against them, because an asterisk (*) will appear next to their name within the system. If you hover over that asterisk for a couple of seconds, you can see the content of the note. To edit, just follow the above steps.
To avoid possible security issues with who can see notes, there is a new setting in Admin > MIS Options. The Minimum User Level for viewing notes defaults to ADMIN, but you can change this depending on who you wish to be able to view the notes. A user-type that doesn't have sufficient privileges will simply not see the asterisk, and will not see the notes field in the record.