What class should I invoke to post to a webform using c#?

I'm having a very difficult time understanding how a c# form can populate and submit a webform. i have been told to read up on httputilities and seen a few others on here but they are leaving me rather confused. If I have 3 textboxes and a submit button : username, password, email; what is the best class to envoke in order to send the form values and submit. At this point I need the program to be able to navigate to a new page within开发者_开发技巧 the same site.

I have viewed the source via firefox for the page in question and I have found the code where I can append it to include "value="something"" and when I load the page (saved as index.html) it will load with that text box filled, does this help me in any way at all?

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HttpWebRequest, check out http://msdn.microsoft.com/en-us/library/system.net.httpwebrequest.aspx