how the rheumatoid arthritis disease occurs in the body .. means what are the causes of this diseases and are there any preventions or cure of the auto immune diseases ??

Your friend is partially correct, 

Rheumatoid arthritis is an autoimmune disease, i.e. it occurs when one's immune system starts preparing antibodies against one's own organs or tissue. The causes may be genetic, infection or hormonal changes. The disease starts with inflammation of the synovial membrane covering the joints. Rough tissue called pannus develops over the cartilage surface and erodes it away. The pannus later hardens and leads to the joints becoming fixed and disfigured. Clumps of lymphoid tissue aggregate over the joints and cause tremendous amount of pain. 

@Devyani- very good attempt. Keep it up! Keep posting!