How Do Birds Fly?

Firing fuel creates a force to launch a plane, like how bird's legs propel itself. Does it mean any flying machines need fuel? Is it possible to engineer an aircraft, a plane, without any kind of fuel? Ok, how do birds fly? It's a good question. So there are two components when it comes to aircraft. There are multiple components, but let's keep it very simple. An aircraft has wings that create lift, that generate lift. They have jet engines or propellers, or whatever. Propellers pull the aircraft forward, and jet engines push the aircraft forward. That's how it works. The flapping of the wings is what gives them propulsion.