How do we pass parameters to the server?

Below are the two ways of passing data to server. The first one shows by using GET and the second by POST.
xmlHttpObj.open("GET","http://" + location.host + "/XmlHttpExample1/ WebForm1.aspx?value=123", true);
xmlHttpObj.open("POST","http://" + location.host + "/XmlHttpExample1/ WebForm1.aspx?value=123", true);