To play ET, or any mud for that matter, you have to be connected to the internet and you have to
connect to the mud via a client like telnet, or via one of the many mud clients available on the net. 

To connect to ET, you have to telnet to its address: et.flynsarmy.com port 9000. 

Then, you just follow the on-screen instructions to create a character.  You begin by inputting the
name and password that you want for the character that you will be playing.  See the help, race and
class pages for more info on creating a character.

A really good, free, mud client is Mudlet.  It lets you connect to many different types of
telnet-based, text games, such as muds, mushs and moos, and to telnet-based chat servers.  Like many mud
clients, it is better than the basic telnet client most computers come with because it offers features that make
mudding more enjoyable, such as color, assignable function keys, triggers, variables you can define, and custom
buttons.