how to creating and adding assembly to source application in c#

Follow steps:
1.create class library with same namespace(ex-AppoloRegistration)
2.Add some class & method in AppoloRegistration.
3.Build the class library code which will produce an assembly with extension(.dll) in your project folder bin(debug folder).
4.Create an asp.net application with same name(vs-new-website-emptywesite(c#).
5.add reference of previous created assembly in your asp.net application.
6.add namespace and use the required class by creating object.

Note:

1. In Solution Explorer, select the project.
2. On the Project menu, choose Add Reference.
3. The Add Reference dialog box opens.
4. Select the tab indicating the type of component you want to reference.
5. In the top pane, select the component you want to reference, and then click the Select button. Press CTRL while clicking to select multiple components.

If you are using .NET 4.0, you can right click in References -> add reference -> In the .NET tab, look for System.Numerics.dll