Use 3D snapping to ensure an exact location for placing points on a model vertex. For example, you can use 3D snapping to help place a surface on a mass that you can later use in the project as a floor or a roof. To enable 3D snapping, select 3D Snapping on the Options Bar.
When you sketch with 3D snapping, curves are placed with driving points which allow for modifications of the curve in the XYZ coordinate axes.
To create a surface using 3D snapping