screw the Raynox DCR-250 filter into the universal adapter, then squeeze in the two spring loaded posts on the outside, that will move the little grabber things on the inside in, then put it so it is lined up with the lens and let out the spring loaded posts, the grabbers should grab the inside of the fz50 threads where a filter would screw on.
You need the universal adapter because the thread size for the Raynox filter isn't the same as the thread size for the FZ50.
I used a FZ30 with this filter for macros last summer, gallery at http://twitch1977.deviantart.com/gallery/
if you're interested!
(shameless plug).
Kurt
Found those on raynox's site, hope it helps.