A site is a unique domain name such as autoparts.com. A store is a 'sub domain' such as ford.autoparts.com or gm.autoparts.com. There is an additional monthly fee and setup for adding additional stores. These fee's are lower than the purchase of an additional site. An additional site is the same monthly fee as your initial site. If you are a multi roof top car dealer with six car makes and you would purchase 1 site with 5 stores.