Don't jump straight in by asking what people are talking about, it's considered rude. This is an example of a chat session in progress. There are several things to point out on this window. The nickname list is on the right, and shows everybody who is in the channel, and the nicknames are shown in alphabetical order. The main channel shows people joining and leaving the channel in green, and people quitting from IRC in blue.
All actual chat is shown in black, and is preceded by the nickname of the person 'speaking'.
The empty box at the bottom which runs the width of the window is called the edit box and this is where you type your messages. Now this next bit may sound obvious, but when you finish typing what you want to say all you have to do is press the enter key, and I only mention this because it is a problem I have seen in the past. The status window shows you system messages. When you perform a Whois on somebody, the results are shown in the status window. The contents of the status window are constantly changing, and they can be distracting for a new user.