Airfoil
An airfoil is a shape curved on top and flatter on the bottom so moving air pushes it upward.
Think of it this way
Hold a flat sheet of cardboard at a slight angle in a breeze. Air hits the bottom and pushes up. Air on top moves faster and presses down less. That gap in pressure lifts the cardboard.
Explaining airfoil by grade level
Look at a paper plane from the side. The wing is not flat. It curves up on top. When you throw it, air moves faster over that curve. The faster air pulls the wing up. That curved shape is what makes the plane fly.