There may be several causes of blood in stool.
First please see this link for understanding the medical terms such as rectum,colon
Gastro-Intestinal Tract (diagram)
Most commen one are
Bright red blood - arise frm the rectum or anal canal
Dark red - comes from the colon
Black colour (malena) - from the intestine or still higher.
Blood mixed with feaces comes from part of intestine higher then the sigmoid colon
Blood on surface of feaces usually come from rectum or anal canal
Blood seperate from feaces may occur when bleeding occurs at some other time than deafecation .(cancer of rectum,ulcerative colitis ,diverticulitis,polyps,prolapsed piles)
Blood in toilet paper is seen in cases of minor bleeding from the skin which may be because of external haemmohoids or fissures.
I hope it helps.
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