block certain user to watch my private channel

I would recommend that you use registration, and you can control access through the web site.

I read the pdf on sdk but i cant figure out anything. how to link a device to my website

That's the missing code that I would pay for if it was available. Both the Roku side and the Website side of the code. Someone one day will make a pay channel hopefully for $1.99 to get that information and watch the channel on how to do it step by step with no errors using the sample SDK like videoplayer and show how to create a form on the website to receive the data or activate Link code or the method for username & password, and get it to sql for both situations for testing if valid or invalid. If no one does it I will make it when my channel is ready.
Then have certain channels that are free and the others are pay. My programmer is close to being done, so it will come out eventually this year.

One big question is what kind of programming languages is the developer familiar with, and wat is available on the website in question. I do my linking in PHP. Some people use ASP. And there are many other server side programming languages. So... what web server languages are available on your server?

We are using php scripts and for the website creation Wordpress. The webserver from Dreamhost is what I use and you can take a look at what languages are supported.