Click "Customize-Customize Floor" to select the floor and enter the customize floor interface, where you could see four sections:
You can add moldings in the left list "Molding". You can add light bands in the "Light Band". And you can find your collected models in "My - Favorites" and your previously used models and materials in the "My - History" catalog.
"Save", "Undo", "Redo", "Molding Brush", "Measure", "Guide Lines", "Clear", and "View".
You can use the draw tool to draw and edit the shapes on the floor. Then you can type in the thickness value for different shapes in the Extrusion input box.
After selecting an object, you can go to the property bar on the right to edit and modify it.