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.