1. ClassInterface attributes
To expose .NET Assembly in COM create a public interface by using methods and properties that you want to expose in the TLB file, and then implement the interface in the class.
Make sure to have [ClassInterface(ClassInterfaceType.None)] before your class so that IntelliSense Features appears in COM.
E.g.
[ClassInterface(ClassInterfaceType.None)]
public class MyTestClass : IMyInterface
2. ComVisible attribute
Setting ComVisible to false makes the types in this assembly not visible to COM components. If you need to access a type in this assembly from COM, set the ComVisible attribute to true on that type. By default it sets to false.
E.g.
[assembly: ComVisible(true)]