Question

For example when you introduce an static class in your source code, csc compiler turns it into a sealed abstract class (Correct me if I am wrong, please).

But how about Interface; Does the CLR knows what an interface is? Or compiler converts it to to some kind of type declaration?

Answer 1

For example when you introduce an abstract class in your source code,
csc compiler turns it into a sealed static class (Correct me if I am
wrong, please).

I am correcting you.

An abstract class such as:

public abstract class Foo
{

}

looks like this in IL:

.class public abstract auto ansi beforefieldinit Foo
    extends [mscorlib]System.Object
{
    .method family hidebysig specialname rtspecialname instance void .ctor() cil managed
    {
    }
}

But how about Interface; Does the CLR knows what an interface is?

Yes, it knows. For example:

public interface IFoo
{

}

translates into:

.class public interface abstract auto ansi IFoo
{
}