Book 1 the boy in the iceberg:

We zoom in on two people in a boat as we can see that they are fishing. Sokka pov: it's not getting away from me this time watching and learn katara this is how you catch a fish. Katara pov: she sees a fish and starts to water bend the fish out of the water. As sokka is too focused at trying to catch a fish he doesn't notice as she floats the fish above his head and he accidentally pops the water surrounding the fish allowing the fish to jump back into the water. Sokka pov: why do i always get wet when you play with magic water. Katara It's not Magic Water it's called water bending. As they began to bicker they are caught in a water tide causing their ship to break and landing on an iceberg, as they continue to Bicker to themselves Katara accidentally water bands a glacier causing it to start to crack as the glacier breaks they get launched away soon after they came to a stop the water starts to glow and a spear of ice comes out of the water they can see a boy encased in the ice. As Katara gets worried she grabs sokka boomerang to break the ice as she starts to hit the ice as it burst a beam of energy is sent out that can be seen by a nearby Fire nationship as we can see what seems to be the captain of the ship talking to his uncle as it seems he has found what he is looking for as he's uncle is talking telling him that it is just the Northern Lights and not to get too excited. We figure out that his name is Prince zuko and off to the side we can see a person in the shadow leaning up against the wall saying Zuko it seems It's Time to find he as zuko looks up and smiles to him yes it is Sasuke. As we go back to the glowing light we see the siblings stand up to see a glowing boy crawl out of the ice has the glowing stops the boy Falls but Katara catches him. And sokka begins to poke him with his boomerang katara quickly stops him. The boy in the ice soon wakes up only to see a beautiful girl hovering over him as he starts talking she leans closer only to hear him say will you go penguin sliding with me. As he quickly gets up confused on where he is, sokka quickly ask him: how did you survive in the ice. as he crawls back into the ice to look for his Flying Bison he quickly finds him to check if he's okay. As he tries to wake up Papa only for him to lick him as he wakes up. sokka not knowing what it is quickly gets sneezed on by the flying bison. As the boy from the ice ask where is he as sokka accuse him of signaling the Fire Nation with the energy being Katara is quick to mock sokka as the boy from the ice does not look like a fire nation spy. As Katara introduces sokka as the paranoid brother. And she asked for his name he begins to sneeze causing a small wind vacuum as he flies up into the air as he comes back down he says i'm aang. As sokka is confused how he flew 10 feet in the air from a sneeze as aang thought it was higher than that Katara quickly comes to the realization that he's an airbender. As sokka is trying to make sense of it all he starts to head back home but quickly realizing he doesn't have a boat anymore. Aang quickly offers them a ride on his Flying bison, Katara gets on but sokka tries to resist but she talked some sense into him. As they get on Aang says Appa yep yep trying to get appa to fly but he is too tired from the hundred year nap so he jumps into the water and begins to swim. Sokka is being salty in the background as Aang tries to defend Appa. As we go back to the fire nationship we see Zuko's Uncle going to sleep after telling Zuko and Sasuke a man needs to sleep Zuko doesn't listen but Sasuke heads inside to go to sleep as we take a sneak peek until why Sasuke is there as his clan was destroyed he was left a war orphan we can see there uncle taking care of him as he was a family friend leading Sasuke to grow up as his second nephew. Sasuke left with Zuko because they grew up together as Brothers as Zuko's sister hog the attention from his father. So that's a sneak peek into why Sasuke's there.