If you need to draw inner walls (such as dividing walls), click the main wall where you want to attach the new inner wall and select Add inner wall from the popup menu that appears:
The Application will insert a new inner wall (with default size) at the position you clicked with the mouse, as shown in the following image:
You can now move the inner wall or resize it however you like.
If you want to change its size, select the end joint and drag it to extend the length of the wall. You can also click on the wall dimension to insert a specific length, as shown in this article.
If you want to move your wall, click anywhere along the wall and start dragging it in the desired direction, as shown in the following image. You can obtain the same result by moving each end of the wall individually, as well.
You can create a new inner wall starting from an existing one: click the inner wall you have just created, and again select the Add inner wall command:
You can now move the inner walls to the needed position, and you can get a niche like the one you see in the following image:
Click here to see how to delete one of the walls.
With this command, the inner walls you've just created will have the same height as the perimeter walls. Click here to see how to create inner walls with different widths and heights.