In general you have to know that a Sankey diagram based on Nodes (Knots) and Streams (Flows). The thickness of Streams based on various amount of components (at least one) and it' s value. That's all you have to know.
This is the symbol for adding a Node at the menu bar.
By clicking this symbol you're able to draw one Node on the pane. When
double clicking the symbol you're able to draw as many Nodes as you like
at once until pressing the button again or pressing ESC button on your
keyboard.
This is the symbol for adding a Stream at the menu bar.
By clicking this symbol you're able to draw one Stream on the pane. Therefore
you have to choose the Node where's the stream come from and than the
destination Node. When double clicking the symbol you're able to draw
as many Streams you like until pressing the button again or pressing ESC
button on your keyboard.
This is the symbol for opening the dialog to add/delete/modify
components and it's parameter (measuring units, and factor which is needed
to weight the component and therefore the amount * factor results into
thickness of Stream).
(Movie time 4:28 min)