How did the avatar in the Last Airbender get picked?

Answer 1

One week after Fire Avatar Roku died after an explosive volcano eruption, Aang was born. The monks have Aang to choose four toys out of thousand of toys. Then Aang chose the Elemental Toys, each from the Air, Water, Earth and Fire. The toys which Aang picked was the toys that the previous Avatars had picked too. And, at the age of 12, the youngest so far, Aang got his Airbender tattoos, which marking him as an Airbending master and developed a new Airbending move. But the Council of Five wanted Aang to go to the Eastern Air Temple to even pursue becoming the Avatar. But Aang fled with his Sky Bison Appa. They got caught in a storm and they were pushed into the ocean by its waves. Fortunately, Aang unknowingly triggered his Avatar State. With that, he made an air sphere which covered him and Appa. The sphere got near the Southern Water Tribe which made the air sphere frozen. That was for 100 years.

Answer 2

In the last couple of episodes in BOOK 2 (Earth), Aang unlocks his chukra allowing him to go in and out of the avatar state, but after Azula "kills" him with a lightning bolt, his chukra is blocked. So the answer is yes he can until the end of BOOK 2....

Answer 3

The monks knew aang was the avatar because when he was little they set 1000 toys in front of him and let him pick 4. They knew he was the avatar bc he picked toys that symbolized the elements and that were toys of the past avatars.

Answer 4

Whenever Aang goes into the avatar state, he was pulled into it by having a strong emotion or flashback. In many cases, Aang was taken out of the avatar state when Katara hugs him, which calms him down and makes Aang face reason. In other cases, he stopped being in the state when he fulfilled what he got into the state for. Example: He gets mad that something of his was harmed (let's say), gets angry and emotional, and once he finishes harming the figure which harmed that something of his, he would calm down and stop. Aang is not able to control himself in the avatar state or when he gets in it. Therefore, he wouldn't be able to control when he got out of it. We are not sure whether Aang learned to control the avatar state later on.