What are the differences between fistula ani, anal fissure and hemorroid? Thank You

Different diseases. Different common ano-rectal diseases. Fissure is crack in anal canal , hemorrhoids are varicose veins like vascular structures protruding from anorectal area under the mucous membrane , anal fistula communicate with a internal opening at anorectal junction to external opening(s) in perennial area . See you doctor will tell your problem.