At the top part of the Networks screen you can find a button resembling the "Play" button of a media player. Next to that is an input line, where you can insert an address to download the server list from. Enter
http://upd.emule-security.org/server.met there and press the "play" button. aMule should automatically download a server list and connect to ed2k, unless the ED2K checkbox is unticked in Preferences>>Connection.