To communicate with other KDE members over IRC, you will need a way to connect to the freenode IRC network. We suggest Konversation. You can install Konversation using the KDE Discover Software Store or using the command line , which differs based on what Linux distro you're using:
See the handbook for help in setting up Konversation, although a convenient alternative if you want to get going quickly is freenode's online webchat. You will need to choose a nick (the name you appear on the network as), connect to freenode and join a channel. #kde is a good first channel to join. This is the central channel for users and contributors to communicate, but most teams will have their own channel.