When a bird soars through the sky powered by its wings, that's flight, the process of traveling through the air.
Humans can experience flight by getting on an airplane or trying out hang gliding. You can also describe each individual instance of flying as a flight: "I took a long flight to Sri Lanka this summer." Anything that's soaring through the air is in flight, especially if it has wings or is engineered to stay up there. As a noun, a flight is also one group or set of steps: "We had to carry her books up three flights of stairs."