FormIt utilizes the concept of Layers to control visibility of objects. Learn more about Layers here
On the Layers tab you can create and name your own layers by clicking the "+" icon. Then select the geometry you'd like to place on that layer. On the Layers tab you can choose from the dropdown list which layer you want the geometry to be on. Finally toggle off the layer you chose. This will verify that you've accomplished what you intended.
Layers are Scene specific. So in any saved scene you can have unique layer states - this way you can create and display different design options in a controlled and pre-set way.
Layers can be sorted by dragging and dropping the layer names in the palette.