Korra defeated Vaatu and Unalaq and saved the world. She decided to leave the spirit portals open so spirits can both go in the spirit and human worlds. Peace was brought back to the world once again.

~Meanwhile~

As Mako saw where Korra was at. He thought to himself.

"I need to tell her the truth. But if I tell her. Would she hate me? I didn't mean to lie to her. I feel really awful about it. I wish our stupid break up never happened. Then we would still be together. But when I tell her. Would she want us to be back together again? I really hope so. I made a mistake. I shouldn't have kissed Asami...

Avatar Aang was raised by monks, although the identity of his real parents was unknown. Being raised by monk Aang was taught about life and to respect it, the ways of the monks are ways of peace and meditation, Aang was already a master airbender before he found out he was the avatar, he learnt and mastered all four elements by the end of the summer. And all his masters were part of Team avatar(katara, toph, zuko). And he was just a kid. Monks are also spiritual people thats why it didn't take Aang along time to master going into the spirit world.
Well in Avatar Korra's case she mastered three...