When you first arrive in the game you will have a number of items on you. One of these items will be a voucher for an object called a talker.
By exchanging this voucher for a talker you will gain access to a MUD wide chat system. The talker can be customised with different colours for different channels and it can be made to echo back your chats so you can make corrections to any typo errors you make.
Talking on a channel is easy; you simply start your input with the relevant word, such as 'assassins' and then enter the chat you wish to make, for example 'ninjas Hello all.'
Channel one has a very poor signal to noise ratio. It is a channel devoted to general chatter and banter and is not normally worth listening to. The exceptions are during major world events when channel one will often be discussing and arguing about the event.
I don't often have channel one turned on because it is very spammy.
Channel (two) is very much like channel one, only with made-up stories from the NPC Sokkard and various players singing. I don't often turn this channel on either although I am assured it can be fun.
The (assassins) channel is accessible by all of the guilds who get the inhume command - the Mano Rossa, the Hashishim, the Ankh-Morpork Guild and the Ninja. This channel is useful as it is where people announce when they manage to inhume a contracted NPCs. Listening for these announcements can save you a lot of time when you finally get to the point where you can inhume NPCs.
The banter on this channel is very Ankh-Morpork focused. This is understandable as they normally have more members online than the other three guilds combined.
The (Ninjas) channel is entirely devoted to the Ninja Guild and although quieter than the (Assassins) channel it often has more relevant information about the guild than (Assassins) does. It is often the first place to ask for ninja-related advice and is a good way to get to know other ninja.
I would advise all ninja to have the (Ninjas) channel on as it will help them to integrate into the ninja guild and bring them into the community.
There are a great many channels to choose from, each with its own 'flavour'. For example, once you have joined the Apex Club you will have access to the (Apex) channel, which is much like channel one.
There is also a channel for the player killers, called (Playerkillers), over which a lot of PK focused discussion takes place.
In Ankh-Morpork there is an NPC who will turn any item you want into a talker for a small fee. He is located off of Short Street and is called Jorodin.