Shops or if somebody know,Stores are the place of where you can buy things for your pets. Some sites haves especific shops (E.G.: One for food,other for toys and whatever).
Go to the edit page of your site (located in "My site" tab) and look for "Shops",then click "Add New Shop" after that,do the things you will do (description,shopkeeper image and name...whatever.).
Adding a item to the shop Edit
Go to the edit page of your site and look for "Items",then click "Add New Item". After that,you choose the item's image,type and other things. Done? Now go down and choose a shop and put the maximum stock of the item. Already made an item? Just go to the edit page and click "Edit Item",choose an item,then go down and select a shop and put the maximum stock of the item.