The general pattern from Web forms -> Win forms:
- Add a WCF service to your Win forms application.
- Implement the interface.
- Use a ServiceHost and start the service somewhere in your initialization code.
- Start your Win Forms project.
- In your web forms project, Select References -> Add Service Reference.
- Enter the URL in the Forms application's config file. (this is added when you create the service) the service should be discovered and proxy code generated automatically.
- rebuild the Web forms project, you should have access to the Win forms service methods.
Services in the other direction are similar, but you don't need a ServiceHost implementation (IIS will host the service automatically)
You'll probably want further configuration as well. Possibly different bindings, and security.