Can someone explain to me why my eyes black out when i stand up?

Many possibilities: Loss of vision on standing (amaurosis fugax) may come from a transient drop in blood pressure which comes with standing, but this often occurs only when there is some compromise of arterial circulation to the eyes. This is never normal. You need to see your doctor and get a referral to an eye specialist if needed. There are many, many potential causes, some of which are very serious.