The applet let's you create graphs and observe some of their properties.
Start creating a graph by placing the cursor in the applet area and dragging it to another location. As the button is released, you'll see the first edge joining to vertices labelled A and B. The labels are provisional and can be either removed or modified at any time by double clicking on a vertex, which will bring up a dialog where you'll be able to modify the label of the selected vertex.
Subsequently, you can start an edge at an existing vertex or join to existing ones. Your latest addition to the graph can be removed by pressing the Undo Last button.
The applet allows for multiple edges joining the same vertices and for loops that start and end at the same vertex. To create a loop, start at a vertex and drag the cursor just a few pixels. A short edge will be automatically converted to a loop. Solitary nodes can be created by double clicking in an unoccupied space.
The labels may be augmented to show the vertex degrees (in parentheses.) This is done by checking the Show Degrees box. When the box is checked, the odd vertices appear as double circles to distinguish from the single circles used throughout for generic vertices.