Rotating a Volume or Group <Back
Click the Rotate button in the toolbar, then grab a volume or group near the visible edge. Drag around to rotate it about its centre in the facing plane. Angle snapping is honoured if set. Holding the shift key constrains rotations to be in multiples of 45 degrees.
Rotating a Face
Rotating a face is done in the same way, except that the face is rotated in-place.
Also, right-clicking on an object will allow you to do in-place 90-degree rotations.