Metz wireless ringflash 15 MS-1

Can someone advise please.
I'm unclear on how this unit works.

I have a Pentax camera without a pop-up flash. If I get the Metz 15 MS-1 do I also need to get a small flash to fit on the Pentax, and then fit the IR adapter onto it?
If that's the case will the adapter fit all flash units.
I've looked at the Metz website, and this still isn't 100% clear to me.
Thanks
--
David