As always in this game series you get a lady card that is filled with game-money and a budget for your shopping.
Walk into the Hawaii beach shops and buy clothes for your character. You can complete a challenge, often by buying a certain apparel/makeuop/hairstyle etc, to earn extra money.
You need to buy clothes before you can dress up your character. After you have dressed up your character then you can save the outfit on your desktop or in a photo album in the game.