Tutorial 4: Making more connections
You've already got a fine diagram, but sometimes you want to diagram relationships that are not strictly tree-like. Let's manually add some more connections. Before you start connecting things together yourself, it's a good idea to turn off the automatic layout feature. Choose Diagram Layout from the Inspectors menu to show the relevant inspector, then deselect the Automatic Layout checkbox. 
Now let's make the Line tool match the lines already on the canvas. Click and hold the Line tool button in the tool palette, and a menu appears. Under Canvas Styles, select the Straight, Stroke: Obsidian entry. Now the lines you make with the Line tool will look the same as the lines that were created automatically by the outline view.
To connect two shapes, just activate the Line tool, click one shape, then click the other shape. Make connections and label them to signify the following relationships: Don John and Don Pedro are half-brothers; Don Pedro and Leonato are friends; Hero and Claudio are in love; Benedick and Beatrice are (eventually) in love. As you do this, free to use the Selection tool to move shapes into more comfortable locations. 
Now that the diagram is more complicated than a simple outline, you won't be needing the outline view any more. Choose Outline from the View menu again to hide it, or just click its icon in the toolbar.