Saw a black shadow in my eye when was focusing my sight in the objet and the other eye was covered. is that normal. am i getting blind?

Usually a floater: It's usually a floater, but if there was also trauma, flashes of light, or increased or larger floaters, loss of part of your vision, see an eye doctor asap. Those are signs that this could be from a serious retinal problem such as a retinal tear, retinal detachment, or retinal hemorrhage, among other things.

See your eye doctor: Depending on how big that shadow is, it's time to see your eye doctor, and have a dilated fundoscopic exam done to see if you might have a possible posterior vitreal detachment, or just floaters in your visual axis. This can't be diagnosed in a forum, but an eye exam is easy to do, and will give you the most information and options. They'll check your vision too!