Below is the screen for making boxes. There is an icon on the left side. Click on that. Click on your document and drag to the size. The size can be adjusted at the top and the fill and stroke can be adjusted at the bottom.
Sometimes with a new version, the box comes out with no fill or stroke so you have to set that up first.
There are good Inkscape tutorial at Scroll Saw Village and at Scroll Saw Workshop.
If that doesn't answer your question please let me know.
