I see blood during bowel movement, what to do?

See a doctor: This can be a symptom of less serious problem such as a hemorrhoid or anal fissure or a more serious problem problem such as a cancer. There are other problems such as inflammatory bowel disease which cause blood in/with stool.

Blood in stool: Well if you are having constipation then you can injure the bowel wall, develop hemorrhoid and fissure, see a doctor for evaluation.