How do you beat Kingdom Hearts 1?

You just keep going through the storyline in each world until you get to 'The End of the World' and beat the final boss (Ansem i think). But you won't likely get anywhere if you don't level up. A lot of battles will be extremely hard to complete if you are at a low level. Just keep fighting heartless to level up. Some bosses such as Sephiroth do not need to be beaten to beat the storyline of the game. The Coliseum tournaments and Whinne the Pooh minigames also don't have to be played to finish the storyline.