I get that:

Warning: include(cel/ugdisplay/code.php): failed to open stream: No such file or directory in ..../member.php(599) : eval()'d code on line 6

Warning: include(cel/ugdisplay/code.php): failed to open stream: No such file or directory in ..../member.php(599) : eval()'d code on line 6

Warning: include(): Failed opening 'cel/ugdisplay/code.php' for inclusion (include_path='.:/usr/lib/php:/usr/local/lib/php') in ..../member.php(599) : eval()'d code on line 6

You did not upload the files in the UPLOAD folder, or else you uploaded them to the wrong place. There needs to be a folder called "cel" in your forum root after upload.

There we go, works. :)

Can I ask what this means?

https://vborg.vbsupport.ru/external/2014/03/36.png

How does one add groups to show up?

Well, that is pretty much explained in the description, is it not? It's a comma seperated list, and you just add the ids of those usergroups that are supposed to see the box, too.
To find out the id of an usergroup, just go to the usergroup manager and look it up there.

BTW: Please ask further questions in the addon thread :)

Oh okay, I just got confused to where it said they will always be shown online. :)

Damn. That happens if you copy text snippets from another addon. Please ignore that, I'll fix that :p

Haha, I thought it was something like that. :P