After passing stool i noticed very tiny and light red spots on my toilet paper. i assume this is blood. why?

Usually not serious: Maybe just hard stool with minor injury. Other common causes are anal fissure (an anal sore) and hemorrhoids (enlarged veins). Usually nothing serious. However, there are other less common causes. If your anal area has been sexually exposed, especially if you are gay, STDs are possible. If the bleeding continues, if any pain. at risk for STD, or otherwise concerned, see your doctor soon.