A human being has two eyes for several reasons:
1. To have a wider screen of vision.
2. To focus properly on any one subject.
3. Each of the two eyes works as a backup to the other one.
4. To see the world around in 3-dimensions.
5. For safety reasons.
So we can are brain can tell how far things are away from us. That is called stereoscopic vision. Two eyes enable stereo vision. By having two separate images, it is possible for the brain to work out distance. This is useful for hunting and escaping from danger.
All vertebrates have two eyes (there is a sort of symmetry of most bodily organs either side of the plane of the backbone). Humans being vertebrates share this symmetry (although the heart and the digestive tract are not symmetric) and therefore have two eyes.