The Worldcon program is built up from interested fans and pros on a wide variety of topics. Every program participant must be a paid attending member of the convention (as are all staff and volunteers) with the exception of the very few Guests of Honor. This is in part because each Worldcon is organized in turn by a different corporate entity, so there is no built in financial continuity from year to year; we must raise the funds for our conference almost exclusively from membership fees. It is also, perhaps as importantly, because the culture of participation is one of Worldcon's oldest traditions; the entire event is an experience created mutually by the entire membership, fans and pros alike.
If you are interested in participating in the program, the first step is to register as a member of Worldcon 76! Be sure to indicate your interest in the questionnaire.