Designing software working system

I'm stuck with an issue where I need to design the entire working of a software system. This includes the following things

1. A customer entity with all the ways that he can access the software.


2. A database/data warehouse representation.


3. Some other small/big entities.


4. An entity representing the system(mostly at the centre of the design but can vary)


5. An accounting and a HR entity.

Now, I know something like this is something like the class diagram but the class diagram represents the classes and the methods used. And I don't need any boring and simple presentation like that. What I need is some really interactive design.

The problem is I do not know the search term to google it neither do I know what shall I call it so that I get proper results when I search anything related to it.

P.S I know the designing tools and software required for it. I'm just not getting the clear picture or a design to follow. Also I can do it entire design myself but still some ideas would be an aid.

Any suggestions?