Complex sentence: The name "Worldcon" is owned by the World Science Fiction Society (WSFS), whose membership are those paying attendees of the convention, which is typically run by local fan organizations who "bid" to host the event.
Split into simpler sentences: The name "Worldcon" is owned by the World Science Fiction Society (WSFS), whose membership are the paying attendees of the convention. The conventions themselves are typically run by local fan organizations who bid to host the event.