Hello, first off thanks for checking it out!
Second, make sure you have the most update to date version.
Once you have that, if you click on add node, you'll be able to select a Scene node. If you have background assets loaded to your asset manager, you can assign a background in the Scene Node. Hit apply and it will display! Just a reminder, any nodes connected after a Scene Node can be collapsed, for when things start getting a little more complex.
I'm still working on the Build function atm. Hopefully I can get that knocked out in a day or two.