2. Ln is the natural log function; it's commonly used in math classes but you likely won't see it until Pre-Calculus or whatever your local equivalent is. If you have a calculator, it'll be the Ln button. You can see it in Scientific View of calc.exe as well.
Or you could just download a regular IRC client; mIRC is the most common pretty much worldwide (http://www.mirc.com). This is best if you intend to use IRC on a regular basis; the Java Chat is mostly just used by new players who want to pop into the help room and ask a few questions once or twice.