Now, we create some thing. Blender has several basic shapes. Att this time, we use a cube. In the object mode, relocate your 3D cursole to your desired location (just left click on anywhere in the 3D window).
Create new cube in accordance with following procedure.

After the creation, the mode is changed to the edit mode and all vertecies are selected.
Well, try to move the 3D cursole outside of the cube.

Create another cube by "Space Key" -> "Add" -> "Cube" (Note: this time there is no "Mesh" in the menu.) Result is shown as below.

Above operation is to add another mesh in the same object. If you move to object mode, these two cube can be handled as one object.

Let's create other shape.
