Two ways:

1. You can process a text  field on same page, look at:
www.learnasp.com/.../pageeventmodel.aspx

2. If you want to send  the value to a different page just place this doe in a button:
response.redirect("otherpage.aspx?" & request("QUERY_STRING"))

asp.NET adds bits to your controls id

check this out

int loop1;
   NameValueCollection coll;

   //Load form  variables into NameValueCollection variable.
   coll = Request.Form;
   // Get names of all forms into a string array.
   String[] arr1 = coll.AllKeys;
   for (loop1 = 0; loop1 < arr1.Length; loop1++) 
   {
    Response.Write("Form: " + arr1[loop1] + "||||" + Request.Form[arr1[loop1]].ToString() + "<br>");
   }
   if (Page.IsPostBack)
   {
    try 
    {
     bod = Request.Form["_ctl1:EmailBody"].ToString();// Note you cannot just Request.Form["EmailBody"]
    }
    catch (Exception ex){}
   }