When you open the 3D window, an editing plane automatically appears: new elements will be placed onto this editing plane.
If you begin element input by snapping to an existing element hotspot or surface, the editing plane will automatically move to that position.
You can reposition the editing plane manually at any time.
During editing, the editing plane may adjust itself automatically. For example, as you drag this roof ridge, the editing plane automatically becomes the vertical plane on which you drag the cursor.