from Vsig manual:
A supermodule is created by
selecting the required modules, and then using the Create
Supermodule command. All connections, connectors and fields of the component modules
will then be hidden, except for those connected to points outside the
supermodule. For this reason it is worth making the external connections to the
modules that will comprise the supermodule first.
You may want to connect all the needed inputs and outputs before creating a supermodule. When you save it, all I/Os will be properly displayed then.
When you "Add to Library" a supermodule, it is saved as.sif. The Library is the place where you want to add Supermodules to have them available for later work as a group of modules in the same list where all other modules belong.