Whenever a plane flies, four invisible forces are pushing on it. Two of them push up and forward (good — that's flying!). Two push down and backward (bad — that's gravity and the air pushing back).
For the plane to stay flying, lift has to beat weight, and thrust has to beat drag. Engines do thrust. The wings do lift. That's the secret.
An aeroplane wing is curved on top and flatter on the bottom. As the plane moves forward, air rushes over and under the wing.
The air on top has to go a longer way (because of the curve). It speeds up. Fast-moving air pushes down less than slow-moving air. So the slower air underneath pushes up harder than the fast air pushes down — and that pushes the whole wing up. That upward push is lift.
Tilt the wing more, and you get more lift — until you tilt too far, and the air can't follow the curve any more. Try it:
On take-off, the plane needs lots of lift — so the engines roar at full power and the pilot tilts the nose up. As soon as the plane is fast enough, the wings lift it off the runway.
Up at cruise (around 10–12 kilometres above the ground), the air is thinner and there's less drag, so the plane can fly fast on less fuel. That's why long flights climb so high.
Landing is the opposite of take-off — slow down, drop little flaps from the wing to keep enough lift at low speed, gently kiss the runway. The wheels squeak. Everyone claps.
Air looks empty, but it's not. It's full of tiny pieces (molecules) that bump into everything. A plane uses the shape of its wings to make those bumps push it up instead of just sideways.
Birds figured this out 100 million years ago. Humans only worked it out 120 years ago — the Wright brothers, in 1903, with a wood-and-cloth glider. Now you can fly from Saigon to London on a Boeing 787 and barely feel it.