In MapleStory, a world is a set of servers that you connect to. Scania and Bera are examples of worlds. Content in different worlds is always the same, but each world has a different group of players and a distinct economy. Please keep in mind that characters created in a certain world usually cannot be transferred to other worlds, so it’s best to find out what world your friends are playing in before you create your character.
Channels are instances of the MapleStory game. Within each world, there are multiple channels where you can play, so if one channel is too crowded, you can move to a less-populated channel. All channels are exactly the same with the exception of the people playing in them.