Image (click to enlarge):

Steps:

1. Click the "New" button on the toolbar.
       
2. If you have an unsaved portfolio open, you will be asked if you want to save it.  Choose "Yes" to save it, "No" to discard your changes and continue creating a new portfolio, or "Cancel" to return to the currently open portfolio.
    

3. A new, blank portfolio will appear.

Optional:

4. Click the root category "New Category", and press F2 to rename it.
    
5. Type in the name of your portfolio and press enter.