The clouds that are shown on a radar map are a satellite picture that has been superimposed onto the map.
The radar data is from various National Weather Service weather radar stations across the country. The satellite cloud data is provided NASA.
The radar and cloud pictures for the USA are free and available to the public through [Intellicast][1] and the [NWS][2] (National Weather Service) websites. Both of these sites will be helpful to you in learning more about both of these features/services.