A new tune may be created using <ctrl-N>, [File|New] or (notice that there are often 3 possibilities).
Enter a title, select key and meter, and select the type of tune (and thereby the clef(s)) you like to create. A one-part treble-clef will probably most often used.
You are put in edit mode by now and are ready to enter your music. See the tutorial for more information.
The possibilities listed here are generated from the score templates.