Click the Sketcher
icon 
from the toolbar, right-click
in the graphic area and select Sketcher from the popup menu, or go
to Curves / Sketcher in the main
menu.
The Sketcher enables you to create and modify entities in a 2D plane. If a 3D structure is currently displayed in your graphical display area, you must select a plane to enable the Sketcher options.
To access the Sketcher:
Click the Sketcher
icon from the toolbar, right-click
in the graphic area and select Sketcher from the popup menu, or go
to Curves / Sketcher in the main
menu.
If a 3D structure is displayed in your graphical display area, and you have not yet selected a plane, select a plane. (The selected plane is displayed in green.)
The Sketcher toolbar is now displayed to the right of the graphical display area.
Important: After you complete your sketch, you must exit from the Sketcher before continuing to other application commands.