The "Appearance" preferences section has three options, from which you must select one.  They each are different ways that the  can appear on the Panel.
The first option, which should appear as your name, will make the applet appear as your name on the Panel.  That is, the word "Users" will be replaced by your username.  In the example above, the user's name is "Johnny Q. Hacker".  If the name which appears here is not your name, you may wish to ask your system administrator how to change your user's name on the system.
The second option is the word "Users" and is what is in use if you don't change your Preferences.  The word "Users" will appear on the Panel to represent the .
The third and final option is a picture (see the example above).  If you select this option, this picture will appear on the Panel to represent the .
You cannot hurt anything by changing the appearance, so if you're having a difficult time understanding what I mean, feel perfectly free to try out the different options.  As this preference says, the "Appearance" option only changes the appearance of the  on the Panel.
