Hi,
You would use EvalScript for that. For example:
Code: C#
//Set textbox "user_name"'s value to "test"
webView1.EvalScript("document.getElementByid('user_name').value = 'test';");
Note that the script would depends on your page. For example, the above code assumes that the ID of the user name textbox is "user_name". Since every page is different, so it is not possible for the WebView component to provide generic method for you to fill the form and submit. You would have to rely on JavaScript code to do so, which you can run from your code by calling EvalScript.
Thanks!