Aircraft fly as a result of and in spite of many forces acting on the aircraft. A force is a push or pull by something on something. When standing we push down on the floor and the floor pushes up on our feet.
Forces always act in pairs, on different bodies, and in opposite directions.
There are four major forces acting on an aircraft in flight. Lift is the upward force allowing the aircraft to fly. Lift counters the weight that is holding the aircraft down. Thrust is the push or pull forward that allows the aircraft to move. Drag is a slowing force.