When the pilot starts the engines, they make a lot of wind. The wind streams under and over the wings, lifts the plane up into the air and keeps it there.
There are two forces working on an aeroplane when it takes off. The force that pulls the plane down is called “weight” and the one that pulls it up is called “lift”. The special shape of the wings reduces the amount of weight working on the plane, which helps it to lift up into the air as it takes off. The lift must be stronger than the weight for the plane to take off and get to a high altitude.
When the plane is in the air, there are other forces at work. The huge engines produce a force called “thrust” that pull the plane forward and make it move. At the back of the plane, the other force is called “drag”. The thrust must be stronger than the drag for the plane to fly. The thrust works together with the lift to pull the plane up and keep it in the air. So, thrust (from the powerful engines) and lift (helped by the design of the wings) must be greater than the drag and weight for the plane to fly. The reason you can’t fly just by jumping and flapping your arms is because you don’t have an engine and special wings!