how to click on web buttons from C# programs?

I've searched a lot about this but as where as I needed a full guide, I decided to ask my question here.

first: sorry for my bad english.

I want to use C# for clicking a web button but I don't know how to do this. what I found was about webBrowser thing and HtmlDocument, however none of them was a useful answer to me.

for example I have a html code like this: ​

please help me from the beginning... :)