SAP NetWeaver is a Java-based stack and its developer edition is available.
In SAP system, Function modules are like web services. They are used to expose the structure of the data dictionary or to expose business objects.
Function modules are sub-programs that contain a set of reusable statements with importing and exporting parameters. Unlike Include programs, function modules can be executed independently. SAP system contains several predefined function modules that can be called from any ABAP program. The function group acts as a kind of container for a number of function modules that would logically belong together. For instance, the function modules for an HR payroll system would be put together into a functional group.
To look at how to create function modules, the function builder must be explored. You can find the function builder with transaction code SE37.
SAP modules are available for SAP customers and you have to take a license if you want to explore full functionalities of SAP system. With a trial license, you can have limited functionalities available in each of the module.
You can refer to our SAP tutorial link to learn more about different modules and their functionalities.