How to use guide lines?

Click "Customize-Interior Modeling 2.0" and select a room to enter the Modeling interface.  Select "Guide Lines - Add Guide Lines" above, click on the side where you want to add the guides, then drag the mouse or type in the spacing distance value to add the guide lines. The guides will be shown as dotted lines and when you use the drawing tools, the drawing could snap to the points on the guide line. You can also draw guides with a rotation angle with protractor guide line (the second option under the "Guide Lines" tool).