The curved shape of an airplane wing causes air to move faster over the top surface. This leads to:

Explanation

Faster flow means lower pressure by Bernoulli's principle, so the pressure above the wing falls below that underneath and the difference multiplied by the wing area provides the lift. The wing also deflects air downwards, and by Newton's third law that contributes lift as well, so both descriptions account for the same force. The pressure above never reaches zero.