How do wireless headphones work?

I would like to get Panasonic RP-WF950 headphones. They're wireless. That's something that would be useful, but how do they work? I know they come with a charger cradle thing, but how do they transmit, and where from? Do they come with a transmitter with a 3.5mm jack I can plug into my iPod? or do I have to connect my iPod to the charger thing? or what?