The sketching toolset allows you to draw 2d profiles, which can be extruded or revolved to create 3d solids and surfaces or to add/subtract volume to/from existing entities. The sketching tools to are available on the Sketch tab of the Mechanical workspace Ribbon:
Sketches are created in the XY plane of the current User Coordinate System (UCS). Since the dynamic UCS is enabled by default you can create 2d entities on the 3D solid face under the cursor. Use the Align UCS tool to position the UCS according to your needs.
Use 2d constraints to make the sketches parametric.