A Note is text which can be referred by other entities.
When creating a note by clicking on
you are asked to enter its content. Notes are by default not
linked to any entity. Afterwards you can add a NOTE property
to any entity and link it to a note by entering its id and pressing
link.
A note according to Gedcom doesn't necessarily have properties. But you can still add information to a note that completes your data. Here is an example:
@N003@ NOTE The author of GenJ DATE FROM 1998 TO 2000