On the Diagram toolbar, click the Note Link 
button.
In the Diagram view, click the source element.
Drag the link to the destination element.
Drop when the second element is highlighted.
The text of notes linked to class diagram elements does not appear in the source code. If you want comments entered in the source code, then in the Properties view for the class, use the description property to enter the class description, or you can enter source code comments directly into the code by using the Editor.
You can use the UML Navigator to view both sides of the link - client and supplier. To change the properties of a note link, in the Diagram view, right click on the note link and choose Properties from the context menu.
To draw a note link between elements:
On the Diagram toolbar, click the Note Link
button.
In the Diagram view, click the source element.
Drag the link to the destination element.
Drop when the second element is highlighted.