Ooh… this is going to test how much of my engineering degree I can remember!
It is mainly to do with the shape of the wings – this shape is called an ‘aerofoil’. The engines are mainly there to create a flow of air over the wings and to keep the plane moving forward. It’s actually easier for a plane to take off than to keep to a certain height!
The shape of the wing causes the air moving over the top of the wing to move faster than the air beneath. This creates an upwards force, called ‘lift’, as the faster air puts less pressure on the wing than the slower air. This is basically how an aeroplane works. You can alter how much lift you get by changing the shape of the wing – you may notice this happening when you fly, as different flaps move up and down.
You can kind of see how this works if you stick your hand out to your side when you are on your bike. If you rotate your wrist you will feel the forces in it, either wanting to push your hand up, or down.