How to build a cube

Right-click on the floor and select the menu OBJECT > NEW

Type a name for your new object

Choose the Meshes menu and then click on the Add button to add a first mesh

Select the line "1 1" and then click on the Edit button to edit your mesh

In the window Edit Mesh, click on the white square and choose an image from the hard disk of your PC.

Choose the CUBE mode to create a cube

Click on the ground of your land: hop a cube appears !

Click on the CLOSE button to save your cube, Bravo!

To continue to change your cube, you do not need to repeat all the steps.
Simply click on your cube and choose the menu OBJECT > EDIT MESH.

You are then directly in the last window and you can continue to change it with many options available ...