Excellent Arduino Ethernet Shield Web Server Tutorial

Using Arduino Networking, Protocols, and Devices
48

You need to replace this with your web page.

          client.println(F("<head><script type=\"text/javascript\">"));
          client.println(F("function show_alert() {alert(\"This is an alert\");}"));
          client.println(F("</script></head>"));
          client.println(F("<body><H1>TEST</H1>"));
          client.println(F("<form method=GET onSubmit=\"show_alert()\">T: <input type=text name=t>
"));
          client.println(F("R: <input type=text name=r>
<input type=submit></form>"));
          client.println(F("</body></html>"));

Then search the request for your variables when it is submitted like mine does for "r" and "t".