From FreeCAD Documentation
- Click Create sketch. This will create the sketch within the just created body. It will be named Sketch.
- A task panel like Fig: MS1 will open where you have to choose to which plane the sketch will be attached.
- Select XY_Plane from the list or select that plane in the 3D view.
- Click OK.
- FreeCAD automatically switches to the Sketcher Workbench.
- The sketch is opened in edit mode: you will see something like Fig: MS2. The X axis (the red line) and Y axis (the green line) of the sketch are indicated, as well as its origin (the red point).