open a web form by window form Button

For what I can understand from your question;

You have a windows forms application with a button on it.
When you press the button you want open a Browser.
This browser has to show a text that has been set from your forms application.

If I understand you correct this should be the solution:

In the button click event of the forms application you could create a html-file on your harddisk. Then you open up the browser with:

Process.Start("iexplore.exe", "file:///filename of the file you created");