To chat in computing terms means to discuss a topic instantly, generally using IRC protocols, over the internet. Client chat programs such as XChat connect to a server such as Freenode where they are able to download a list of available channels. Users can then join a channel and, depending on the channel and server rules, initiate real-time conversations with other users on the Internet. For chatting with one person, you will typically chose the ICQ chat protocol, for chatting with a group of people, you will chose the IRC protocol.
Chatting is ideal for beginners and gurus to exchange knowledge. Here's an example how you do it: