Care Notes is a section on a Patient's profile page where you can write any information regarding the Patient, by clicking on "Edit Notes" you will be able to write information in and use tools to make text Bold or change the colour, even add pictures.
Once you have put all the information in there and made it look how you would like, you can click on "Save" and it will keep it on their profile until you decide to remove/edit it.
You are also able to print these notes out so you can pass them to carers or store them in a file if needed.
In Settings -> Account Settings, if the box marked "Show Patient Notes on Mobile App." is ticked, then these notes will show on each visit for that Patient on the mobile app. For instance, you might use it to store a keycode.
However, if you want notes to only appear for some visits for a Patient, e.g. only for morning visits and not for afternoon visits, this information would be added on the repeating visit instead, see How do I add a repeating visit?