There are several different things for you to choose to play in
Winx Club: Mission Enchantix. The first thing that I started with (simply because that's where I almost always start in a game) was Story Mode. The first thing you do is choose how difficult you want the game to be. After that, in Story Mode, you will follow your favorite Winx Club girls, Bloom, Flora, Stella, Musa, Tecna, and Layla. While this might sound like a day at the beach, these girls are about to have some serious work to do. It all starts out easily enough. Bloom is dreaming about a mysterious man. This level is basically a very easy board where you'll learn the controls and get used to playing the game. After you complete this, you'll get your choice of which Winx Club member to help next. It really doesn't matter which one you choose since you will get to all of them eventually. These are all tutorial levels. You must beat them before you get to the main story.
Each area in the main story has several levels to it and most of them end with a boss level. Each level (and the tutorial levels as well) has 50 tokens that you can collect as you go along. At the beginning, these are pretty easy to find, but the further you get in the game, they become increasingly more difficult to locate. You can always replay a level if you missed some tokens. These token unlock things like clothing, music, and movies. Eventually you will complete the Story Mode.
When you get bored of Story Mode or just need something different for a while, you can choose to play in the Arcade. Each of the six Winx Club gals has her own mini-game for you to play. There is a very wide variety of mini-games, so you'll probably like some and hate some. Personally, I thought that it was a good selection of games.
The other two selections that you can choose from the Main Menu are A/V Club and Magic Closet. The A/V Club is where you go to view all of the views and music that you have unlocked by collecting tokens. In the Magic Closet, you can dress the Winx Club members up in the various outfits that you have unlocked with tokens. This does not change how they look in the game, though. It is only for you to view inside the closet. When you are inside the closet, be aware that you will have to hold your DS sideways. It flips the screen so that you can see the full outfit easier.