Birds are one of the most interesting animals in the world. First of all, they can fly, amazing. Second, they often have their eyes on the side of their head, not on the front as we do. This means that they see in a very different way to humans.
Of course, not all birds are like this. While parrots and pigeons have their eyes on the side of their head, owls are closer to humans as they still have two eyes in front. As we know from experience having two eyes on the front of your face is useful. It allows us to understand the depth of objects and allows us to perceive three dimensions. If we had just one eye we would struggle to know how far away our glass of water was and probably knock it over all the time.
Having two eyes in front has its limitations too though. Look straight ahead right now and examine how far to the sides you can see without turning your head. You can see about 120 degrees, less than half of what is around you. This leaves you susceptible to being surprised by anyone comes from behind.
This is the reason that many birds have eyes on the side of their head. It opens their field of vision to about 300 degrees and allows them to see everything that is happening. Have you ever walked behind a pigeon and it noticed that it immediately flies to the air, this is why. This allows birds who face predators to escape with ease as they always see a threat coming. Owls as a predator bird evolved with two eyes in front as they did not need to worry about what was behind them and they had the extra advantage of being able to turn their heads a lot. Owls use two eyes to focus in on their prey and understand with great detail where it is, allowing them to swoop down for the kill.
Of course, having eyes on the side of your head means you cover a greater distance but that your eyes are rarely looking at the same thing (there is a small field of vision where parrots and pigeons could focus in front of them). This means that these birds are often not seeing in three dimensions.
Would you rather have eyes on the side of your head to help you see more, or do you prefer being able to see in 3D?