Q: is it ok that that when i lifting heavy stuff the veins pop out of my arms...(i am 13)

A: Yup, that's perfectly natural and normal. When you perform intense physical activity, the blood flows to and from the muscles doing the work increases filling up the arteries and veins. Blood carries oxygen and nutrients to the muscles allowing them to do work and carries back the 'waste' products of muscle metabolic activity. The effect is usually most visible in forearms/hands where the veins are nearest to the skin.