This type of workflows is like an open set of functionality that can implement many different actions. In reality it is a simple and defined way of enhancing the workflow system without going through the trouble of adding a new screen (not that that is very complicated but this is easier).
So with custom functions we can find a lot of different options and operations to activate on our records.
The steps are:
create a new workflow and select the main module
give it a name and set the conditions
create a new task and select the “Invoke Custom Function” task
On the configuration screen we will find a drop down select box with the available functions for that module
Simply select the function and save
that is it, there is nothing to configure as these are atomic action functions, everything they need to know is given to them by the save context.