A few things in chat will jump right out at you. First, when there are a lot of chatters in the room, the text will scroll quite fast. It may take a minute to get used to, but you will in no time. You may also notice that people tend to use abbreviations for frequently used phrases. A .wav file is a sound file.
Chatters can play sound files that others can hear.
In order to hear the .wav file, you must have it on your computer. So you'll sometimes see chatters swapping .wav files. You'll probably want to try playing and listening to some sound files yourself. The best way to understand chat, much like anything on the Internet, is to simply dive right in. Just relax, have some fun, and make some new friends.