Desktop Notes allow you to create a new note in several ways:
A new note will be created according to your default note settings unless you want to change its appearance by clicking on the spanner icon in the upper right corner of the note.
After you select your note color, font and other settings, click on the "OK" button and start typing your note.
You don't have to save your notes, anytime you click outside the note, it is automatically being saved and when you want to continue typing it again, just double-click the note.