After Sora's world was destroyed, he ended up in Traverse Town, a place where people end up when their worlds are swallowed by darkness. While Donald and Goofy are searching for Leon, Leon happens to find Sora and explains to him the situation. When they are attacked by heartless, Sora gets separated from Leon and meets Donald and Goofy. They're attacked by a powerful Heartless called Guard Armor and quickly defeat it. Donald and Goofy ask for Sora's help to seal the Keyhole to the heart of each world. Since Sora is in search for his friends Riku and Kairi, he agrees to join them and moves on to one of the next worlds...
Next world is Wonderland or Olympus Coliseum, It can go several orders but i reccomend that u follow along...