The PC game is different from the GameCube/PS2 console game.
It follows the story of the DVD movie, Bratz Rock Angelz, through nine objectives. The odd-numbered objectives (Chapter 1, 3, 5, 7, 9) are reflex-like mini-games, where the player has to do the tasks to collect points. Each mini-game has four rounds. When the player takes or misses the part, he'll/she'll gain lower points, at three misses, he/she has to do the round again losing amount of points. With points, the player can unlock fashions for the Bratz girls, except in the final objective.
The even-numbered objectives (Chapter 2, 4, 6, 8) are puzzle-like adventure games. The player has to play with the certain Bratz character and take things to solve a puzzle (for example give a camera to a colleague). The player can take pictures on those objectives to print them on the "Secrets" menu. Each adventure objective, the player has to design an article, logo, flyer, or poster to complete the part of the objective. The player can even print his/her design. This part can be accessed on the "Secrets" menu.
When the player has beaten the game, he/she unlocks a card game, called Top Trumps, which is similar to War. The player gets a card each turn with number totals on it. The player has to guess which number on the card is higher than the opponent's card. If he's/she's correct, he/she wins the card. He/she goes on playing until all 28 cards are in one players possession.
Source: Wikipedia, "Bratz: Rock Angelz (video game)", available under the CC-BY-SA License.