A warrior-to-be, 15 year old Sokka is a very physical type of person. He prefers weapons to Bending, and even if he could waterbend he probably wouldn't change his mind on it being weird. Not much of a believer, he's quick to judge others and can often be a little cynical until proven wrong (like Appa's ability to fly). He trusts his instincts first, but when he makes a mistake he isn't afraid to admit it. He's also been known to be a bit sexist, especially when it comes to gender roles. Although he's learned better, with help from Suki. He's very protective of his younger sister Katara, and treasures the boomerang given to him by their father.
On Kyoshi Island he suffered a crushing defeat from Suki and the other female warriors, but in a true show of character and integrity, Sokka humbly asked for her to train him. Although his training was only for a day or two, he learned enough basics to be able to stand up against Suki and defend against Prince Zuko, if only for a moment. He still has far to go though, but he's getting better. Also on Kyoshi Island, he received his first kiss (did you see the way he blushed? Had to have been one of his first few) from Suki at the end of ep4.
While traveling through the Earth Kingdom with Aang and Katara, they came across an old friend of their father's, Bato. While they reminince about the past, Bato reveals that he is awaiting a map from his comrades that will show the Water Tribe's rondezvous point, which is where their father is. While the two are eager to see their father again, they realize that they are most needed with Aang, and helping him get to the North Pole. They hang on to the map though for future reference.
Still with Bato, he takes Sokka out to Ice Dodge - a rite of passage for Water tribesmen when they turn 14, that tests one's wisdom, bravery, and trust. Since Sokka was too young before his father left for the war, he never had a chance to. Although since they're not in the arctic, instead of weaving a boat between icebergs, they must dodge giant rocks jutting out of the water. Sokka was in charge of steering and calling the shots. With his judgement calls on which way the boat should go and what actions Katara and Aang took to make it happen, Sokka earned the mark of the Wise, which was the same mark his father earned.
Back in the Southern Water Tribe, Sokka became his tribe's last defense when his father left with the other men to fight in the war. He took the task very seriously, and even built a number of snow watchtowers around the village. Although Sokka has the spirit of a solider and the courage to stand up to any enemy, he lacked the skills and technique that would make him a formidable opponent. That won't stop him from trying though, especially if his friends need help. And now, thanks to more training and his experiences while traveling, Sokka has become a much better fighter. Not great, but he's getting there.
Sokka was wary of Aang at first, but he has grown to trust him and is now rather protective of him as well. Although because of certain foolish mistakes on Aang's part, Sokka does not entirely trust him, and his loyalties are always to his sister first. Sokka despises the Fire Nation through and through and is eager to kick their butt whenever given the opportunity. Traveling along with Katara and Aang, Sokka brings dry humor to the group and always gets the best lines. XD