In general I'm not seeing documentation for any of the Samples, but generally you just run them and see the result. Can't do that with the DemoAddin dll. Don't know how to get SolidEdge to see it.
What programming language? The .NET version of the DemoAddIn is documented\commented pretty well I thought. Once I hear back from you, I can assist further.
The first 6 lines of DemoAddIn.cs are code comments to help you get started. The key to registration is to use Package Manager Console commands. The available commands are documented in Useful Package Manager Console Commands. My video Solid Edge Community Templates Quick Start demonstrates how to use the Package Manager Console commands.
If you do not see the Package Manager Console in Visual Studio 2013:
Navigate to Tools -> NuGet Package Manager -> Package Manager Console
I'd be happy to spend some Skype time with you if you still need help.
Okay, knowing I'm supposed to use those lines at the top was helpful. I saw those and assumed it was stuff about getting packages. I had no clue I was supposed to type them. I'll figure it out tomorrow. One thing to confirm: it will work with ST8?