Thanks Omoshu, but this is a rather technical version of what it does, so let me explain it much simpler:
The @Override above a function simply means that OSBot will use this function instead of the default function that's defined in the Script class (the one our script is extending from). You can also call the default function by doing the super() function inside of the function you're overriding (well it's useless in this case, because the Script class functions are empty).