I wonder if I should not try to add the add-in.

The reason I thought I had to was due to the instructions:
7. Istruction:
Build and test the COM add-in. To do this, follow these steps:
a. On the Build menu, click Build MyCOMAddin. Note that building the COM add-in registers the .NET class with the COM interop.
b. Start one of the Office applications that you selected as host applications for your add-in (for example, Microsoft Word or Microsoft Excel).
c. After the add-in has started, the OnConnection event is fired, and you receive a message box.

Well, I started some office applications and nothing happened.