Why can't people use artificial wings and fly like birds?

A bird's entire body is specially formed for flight. It has very large and powerful breast muscles to move its wings, and a keel-like, projecting breastbone to give these powerful muscles a firm attachment. Parts of the body that are not used in flying, such as legs, are reduced in size. Birds are also light in relation to their size; much of their bulk consists of feathers. hollow bones also cut down their body weight.
Man is adapted to life on the ground. he does not have the body features that enable birds to fly. In order to fly with artificial wings, a man would have to built somewhat like a turkey or ostrich.