Moving Single Segments»
You can move a single straight segment using the Contour tool without even selecting it. Position the mouse cursor on the segment line somewhere between its nodes, press the mouse and drag. If you drag the segment close to its ends, only this end with the node moves. If you position the mouse cursor on the middle of the segment you will move both segment ends.
While being dragged the segment will snap to the other objects (if they are visible), where that feature is activated (View > Snap menu). Press Ctrl at any time when dragging selection to temporarily disable snapping.
Moving a single curved segment using the Contour tool will always change the curve form. To move the curve without changing its shape, first select it.