Colostomy is performed by a surgeon. This is done in cases where a patient needs to have part of their colon removed such as in ulcerative colitis, or colon cancer, or diverticular abscess, or disease. Basically the surgeon removes a portion or all of the colon and the remainder part of the colon is pulled up to the skin wall and sutured into place.
Now, a person can actually live a totally normal life with a colostomy. They have a bag that covers the stoma in order to collect the stool and they just simply empty out the bag when it's full. So they can lead perfectly normal lives with a colostomy.