At the start of the game, you can see everything Mummy Pig has asked you to buy. Once you know all the products you have to put in the basket, you can begin walking down the supermarket aisles. In each aisle, you have to grab the items on the list out of all kinds of fruits, vegetables, and other products.
Be careful because Daddy Pig will fill the shopping cart with things you don't need, and you only have space for the things on the list. If you need more space, you have to empty the basket before passing the item you needed to find. If you don't have time, you have to go around the whole supermarket again.
Once you have the cart filled with everything you need, you can go to the register to pay. Make sure you have everything on the list or Mummy Pig will be angry. But the more things you get right, the less angry she'll be.