In python we have a modules but in c# language what is module called.

Answer 1

In C# it is a library. It can contains multiple classes.
To import it's functionality you need to use a using statement.

For example
Using system.io;

To import functionality regarding file handling

Answer 2

I am not sure, but I would think of package, because Java uses that term a lot, and C# is very similar to Java.