The power for ordinary people to fly in the air was introduced by Tien, Chiaotzu and the Crane Sect in the first part of Dragon Ball . Initially, the ability to fly was simply hovering above the ground, not flying freely like it does now, but it was determined to be quite useful. With good control of Ki, humans can do this.

As for Goku, he could fly by spinning his tail when he was young, but this ability quickly disappeared when his tail was cut off. Goku then used the Scale to move in the air. However, how Goku can fly using his own power has not been shown clearly, which makes many people question how and why Goku can do that.

When and how did Goku learn?

As a skilled fighter and master of using his own strength and Ki, it is very likely that Goku’s flight power was activated when fighting Tien. After seeing students from the Crane Sect using this technique, Goku imitated it (like how he learned the Kamekameha technique).

At the end of the first Dragon Ball we see Goku using his ability to fly against Piccolo’s son at the World Martial Arts Tournament. This was some time after he trained with Kami for several years. By the time of Dragon Ball Z, Goku has completely mastered this power, and it is likely that he was already performing it well when Gohan was first born.

In addition to Goku, his best friends Krillin and Yamacha are also said to have learned the ability to fly around this time. It seems that God’s training made it easier for the Z warriors to use Ki, thus allowing them to fly and use other powers. Thanks to that, flying is now a basic skill that everyone knows in Dragon Ball .