The list dialog is the central point for dealing with the different graphs of a plot. Here you have an overview of all graphs and you can manipulate them. You can reach the list dialog via the Edit->Graphs menu or by double clicking inside the plot.
With the buttons "Add Datafile" and "Add Function" you can add a graph from data or function to the plot. (see function dialog or data dialog. ) With "Delete" you can easily delete the seleted graph. With "Change" you can change the settings of the graph.
The "Export" button dumps the graph into a selected data file and the "Edit" button gets you to the edit dialog. Here you can edit the data of the selected graph.