Hey Mohammad,
It is very good to see someone so excited, and asking questions :),
Now for your queries,
1. The intermediate questions are based on the knowledge of Rapid curse,
But comparatively, intermediate will provide you with a deep and better understanding of
these topics and will help you to know the concepts in depth,
You can follow the intermediate and advanced learning paths to understand them better.
2. It is the default action for Mendix to create IDs for their reference,
You can see the built-in database, see, you will notice that for every object there's a
Unique Object ID associated with it.
And for associations, as soon as you create an association between two objects
Mendix itself assigns foreign and Primary keys in the table it stores.
3. The table will store the data of the employee along with the foreign key of the
department it is associated with, as soon as you update the employee's department,
it will automatically update the foreign key itself.
4. The users are stored in the System.User object, if you want to see all
the users in the app,
You can just put a menu item in the navigation tab and on-click show a page,
And set it to show the " Account Overview" page. it will start showing, all the
accounts in your application.
5. Yes, Mendix also uses Relational database tables,
If you want to view the tables,
Run the application
go to console -> more options-> start built-in Server
You can refer to the following image for reference,
Let me know if you have more questions,
Hope it helps!!
**Edited**