How can I modify the drawing surface?

By default the drawing surface will be the most visible main plane.

When using an inking tool, the Drawing Surface controls appear onscreen.

Edit
During edition, drag the axis or use the +/- buttons to translate the drawing surface.

Lock
When locked, the surface can’t be modified.

XYZ Plane / Camera
Choose whether the drawing surface should be parallel with the most visible main plane or should face the camera.

Add / Clear Constraints
You can specify constraints through wich the working surface will pass.
Long press during 1 second to add a point constraint. You can add up to 3 points to constrain the working surface.

When selecting a stroke, Long press during 2 seconds to retrieve the plane used to draw this stroke.