Double-click in the background to create a new node. Create groups by selecting nodes and invoking Ctrl-G; Ctrl-Shift-G to ungroup a selected group. A selected node will have four orange triangles that when clicked will automatically copy the node and link to it. Use the context menu to change the shape, color, thickness, and dashed-ness.
Links can be drawn by dragging from the side of each node. A selected link can be reconnected by dragging an end handle. Use the context menu to change the color, thickness, dashed-ness, and which side the link should connect with. Press the F2 key to start editing the label of a selected link.