Click on the Niffchat button, type your username, and then select with or without smilies. The first time you do this, a security popup with come up, asking for verification. You should be able to click Allow. Then that's it, you should connect. You'll need to explain what doesn't work about that last part. Or you can use another chat client like Chatzilla, mIRC, XChat2, or MirandaIM. Just make them connect to irc.esper.net and then type '/join #niffchat'.