Level
You first need to attract Petula to your village in order for the Paper Pets store to open. You must have at least level five to accomplish this. You can reach that level through romancing other pinatas, gardening and building up your garden and village. Make sure you earn coins when selling crops and other items; you will use these in the shop when it opens.
Village
While leveling up, build your village to have a variety of buildings to occupy your attendants. Petula will only appear in the village. After you meet all the requirements, you will find Petula walking around your village square. Talk to her and her shop will then appear in your icons.
Icon
In the top-right corner of your screen you will see the Paper Pets icon. Arrow up to this icon with the arrow key or joystick. Hit "A" when the icon is lit up and you will find yourself in the store. A number of items are available in the shop, depending on what you need. You need coins to purchase the items. Regardless of where you are in the game, after you run into Petula, the Paper Pets store icon will appear in the menu at the corner.
Accessories
Accessories are the best items in Paper Pets to attract other pinatas. Click the accessories buttons to see what you can purchase for your pinatas. The more accessories you purchase, the happier they will be. When they are happy, other pinatas will see this and come to your village or garden.