Why would there be blood in my stool? What does it mean if there is blood in one's stool? How can this come to be?

Blood in stool can . Have many causes: hemorrhoids, anal fissure, diverticulitis, polyps, inflammatory bowel disease, trauma; black tarry stools may come from bleeding in upper part of GI tract, from meds like pepto-bismol or activated charcoal; iron supplements, blood thinners can also cause GI bleeding. See fp or GI specialist for exam; may need sigmoidoscopy or colonoscopy or egd.