mIRC is an IRC client. IRC is Internet Relay Chat, a kind of network designed specifically for real-time communication. mIRC is perhaps the most famous program of its kind.
All you need to start communicating is to connect to the server and join the channel. The names of servers and some channels are already embedded in mIRC. By default, the server is selected randomly. Then everything is simple - choose a channel and begin to communicate. In the right part of the window there is a list of people present in the channel, and in the left - messages
You can communicate with an individual or even create your own channel and become the most important there. In addition to the basic functions that are actually the shell of server commands, mIRC provides a huge number of different side effects, for example, launching script-s when connecting to a server or filtering flooders actions (people who intentionally litter channels).
Details - both about the program itself and about IRC, can be found on the program’s home page.