The Open a graph block allows you to pass the Sotryline from one graph to another. For this reason, it is very useful when you want to create recurrent and complex systems such as battles or roll of dices.
The graph has to be part of your module or in the global graphs' section : otherwise it will not work. You can create a graph by clicking on the "add' button of your module's menu, or you can "Blackbox" a whole graphic (select blocks, then right click and click on the corresponding element).
In this screenshot, one can see that using the "Open a graph" block allows a clearer organization of your graphic. You can also set different outputs of a graph by clicking on the "out" block of your graph and add different outputs. It is also possible to set different forms of output, such as a flow output, a text or an image.