On installing a new custom theme you should also follow the post installation steps from the theme post installation manual included into the shop archive (as, for instance, Post-Installation-Settings-en.pdf). So it says in this manual that to get the demo pages displayed one needs to add a new user page called 'demo' following the steps below:
1. Navigate to Pages -> User Pages and press the orange triangle on the left, then go to
Add new page.
2. Add demo to the Name field
3. Set Internal for the Link Class field
4. Add demo to the Internal Link Alias field
5. Add #TEMPLATE-ID Preview to the HTML Title Name field
6. Add demo to the List Name field
7. Set default for the Layout field
8. Set Hidden for the Visibility field
9. Press Submit.