Errr... How are you reading this then? Never mind :)
If you are using unix then type:
on the command line.
If you are using a Windows based telnet application of some sort, then
set the address as 'discworld.atuin.net'. Windows comes with a standard telnet program, but it is pretty hopeless (just type 'telnet' at the command prompt). I would recomend you get hold of a mud client, links are provided in the 'Getting Started' section of the website.