So you want to join the guild Nightmare Knights?
The best way to apply is to use the applications feature on the main Tibia website and apply directly to the guild. You will also need to send a letter in game mentioning your interest to join and that you have applied to the guild on the website so I know you have already applied and are interested in joining. Please send this letter to myself, Lord Karr.
Tibia is a very different game then it was when NK was founded. Guilds in particular have changed and NK has grown to be less formal and more of a guild of old friends. We still invite new players to join us, but most of us don't play as much. NK is especially interested in bringing in world trade merchants and other economic aficionados.