I use it for chatting all the time. Used it for downloading a long time ago but I have since switched to other methods.
As for what it is, IRC is short for "Internet Relay Chat" Wikipedia says it is:
Quote from wikipedia
a protocol for real-time Internet text messaging (chat) or synchronous conferencing. It is mainly designed for group communication in discussion forums, called channels, but also allows one-to-one communication via private message as well as chat and data transfer, including file sharing.
As sosseres says,
Quote from sosseres
some streaming sites use it for the chats. It is still one of the most popular chat platforms when you want large channels.
It is mainly considered complicated because you have to find the server and channel you want to go to as well as find an application for it. Navigating these requires some basic commands. That really is more daunting than actually difficult though. Recently, however, a lot of people (including myself) have been using webchat apps which you can just open in the browser. Just plug in the name of the channel you want to go to and it is pretty simple (That only works for chatting though. The more complex functions such as dling require certain IRC based applications and knowledge of a couple more commands)
I hope you try it out KaoriNite