You can create and edit 2D and 3D geometry in part mode. The 2D and 3D buttons in the status bar determine the design mode. When you create a new part, it opens by default in 2D mode. You cannot activate 3D mode until you create 2D geometry. When you switch from 3D to 2D mode using the status bar, you are prompted for a planar surface or a datum plane to position the sketch plane.