There's actually a forum here dedicated to Gluten free dieting. You'll want to try that out - you'll get faster responses than posting here in the journalling section.
For the miniversion:
http://en.wikipedia.org/wiki/Gluten-free_dietYou need to avoid wheat, barley, and rye. Gluten is a compound inside the grains that is crucial to the breadmaking process - it's like a glue - sort of. I understand that there may now be ways of making bread that do not use gluten, but I am unfamiliar with them. It will take some hunting on your part and talking to some folk with gluten allergies or Celiac disease. I do know that Rice and Rice Flour are going to be your best friends.
Also, you'll have to read labels on any prepared foods. Gluten is everywhere, as a sweetener or just as part of the grain itself.