The first box is for adding other parameters (such as shown) and in the second box you'll see the generated commandline string when you push "Show Cmd Line".

Note: only add parameters if you're sure about them. It's just like I already mentioned: leave it alone if you do not know what you are doing.
If you add unsupported parameters, or even worse, forget the leading "-" or "--" of a parameter LAMEr will probably act strange and you might get even stranger results.