You should select "wysiwyg editor" as Type and a suitable Location. My problem is that I can't get it to work myself

I didn't write the extension ...
EDIT:
If you use PHP before version 5.2.5, you need to replace "$trace = debug_backtrace(false);" with "$trace = debug_backtrace();" in the function functionalCallBonusfieldsHook in the file extensions/bonusfields/hook_bonusfields.php.
I still didn't get the Wysiwyg to work, but at least I got the text area... After switching to Wysiwyg in "My Info" I got the wysiwyg editor. (I normally don't use it.)