c# and assembly relation

The question is, well… isolated from the reality. C# does not "communicate with assembly". This is a computer languages understood by the compiler (csc.exe) use to create an assembly.

As you already start moving in wrong direction about understanding the very basics of technology, I would advise you to start reading about .NET from the very beginning.

For example, start from here:
http://en.wikipedia.org/wiki/.NET_Framework[^],
http://en.wikipedia.org/wiki/Common_Language_Infrastructure[^],
http://en.wikipedia.org/wiki/.NET_assembly[^],
http://msdn.microsoft.com/en-us/netframework/[^].

Maybe, even deeper:
http://en.wikipedia.org/wiki/Compiler[^],
http://en.wikipedia.org/wiki/Computer_language[^],
http://en.wikipedia.org/wiki/Platform_%28computing%29[^].

—SA

Assembly in .net
try Google........

Do you mean referencing an Assembly to use from your code?
Right click on your project then click "Add reference" from the menu. Browse all available .NET or COM assemblies. You can also locate other assemblies using the Browse tab or select other Projects in the same Solution.
Pick one or more, click select.
In your code you can now call this assembly by calling the reference with it's full namespace.
For example:

// Create a new Object of type MyAssembly.MyType, from your other assembly.
MyAssembly.MyType t = new MyAssembly.MyType();
// Use any public Methods on this assembly.
t.DoSomething();

So from there it works the same as for normal Classes :)