How to find data in browser form displayed inside C# application

Question

The Webform in C# lets me construct my own browser. I am able to navigate to the site I want to go to. I would like to use some of the data displayed in the browser form in my application. I cannot find any documentation on how to access the undelying HTML. I would like to be able to read the displayed HTML and also add data to the data entry fields before submitting the next URL.