What does the appendix do?

Not much: Except causes appendicitis and generates surgery for surgeons.

Vestigial organ: By and large appendix has no function and its removal does not cause any untoward affects in the human body.It is theorised that in ancient man appendix had a function in absorption as humans could eat bark of a tree but new research from oklahoma state universaty reveals that it plays role in fetal stage around 11th week has endocrine cells .These produce biogenic amines&peptide hormones in fetus.

Immune system?: Researchers believe that the appendix does serve a function as part of the immune system. Others feel that the appendix is a vestigial organ, once used as part of digestive process.