Newbie looks for Info about Nunit Tests For Docker (IIS and Custom App)

Hello I am realy new on docker!
What i will try to do is:

Create a container with custom Software (webService for IIS) .

And i dont really understand how do it.
Far away i need to tests this custom Produkt with Visialstudio Nunit Adapter v3 (Different Tests DLL’s).

Have i Build only one container that contains all this futures (Custom Produkt + IIS + Visual studio)?

I would like understand Docker little bit more
For any Idea I would be thankful!

Best Regard