This is a short and more simple explanation of how planes fly, made for people who don't want a full detailed explination.
How do planes fly?
Simply planes fly by having their wings angled in a specific way that raises the pressure
under the wing, and lowers the pressure above the wing, this then generates lift moving the plane upwards.
For this to happen, thrust is needed to make the air around the wings move and cause the pressure difference.
The more speed and wingspan you have, the more lift will be made.
Enough lift is needed to overcome gravity, and enough speed is needed to overcome the drag on the plane, this is what makes it difficult to make very large planes. When a plane is larger it needs more wingspan to lift itself, but more wingspan and size will cause more drag and slow the plane down.