Click Construction
Geometry 
on the Sketch toolbar.
Select the For construction check box in the PropertyManager.
You can convert sketched entities into construction geometry to use in creating model geometry.
To convert one or more sketch entities to construction geometry:
In an open sketch, select the sketch entities to convert.
Do one of the following:
Click Construction
Geometry on the Sketch toolbar.
Select the For construction check box in the PropertyManager.
To convert sketch entities in a drawing to construction geometry:
Select the sketch entities that you want to convert and use one of the following methods:
Click Construction
Geometry on the Sketch toolbar.
Click Tools, Sketch Tools, Construction Geometry.
Select the For construction check box in the PropertyManager.
Right-click any selected sketch entity and select Construction Geometry.