How I can get the C# interactive window? I have Visual Studio 2015 CTP 6 installed.
And I installed Roslyn, according to these instructions.
According to blog post Using the C# Interactive Window that comes with Roslyn, now I should see C# interactive at
View -> Other Windows -> C# Interactive Window
Update (Nov 2016): It appears that the C# Interactive tool window has been reintroduced. I am using VS 2015 Update 3, which has it; but it has possibly been reintroduced with VS 2015 Update 1 already.
You missed the fact that the blog articles you link to were posted back in 2011, where VS 2015 was not even on the horizon yet. These articles applied to VS 2010 and (I assume) a very early version of Roslyn.
By the way, CTPs are preview versions of a product. As long as a Microsoft product is in the CTP stage, it is subject to the possibility of rapid and even short-term feature changes. So even if these articles did apply to VS 2015, they would have to be about the exact same version of the product that you are using; otherwise you would have no guarantee that they contained up-to-date information.
It appears the C# Interactive window worked for VS 2010 and VS 2012, but was no longer supported in some later versions of VS.