"Account" services are used to create an account for your personal use and to update your personal account settings.
"Customer" services are used to create an account on behalf of a customer. In reality, your customers may already have accounts and may simply wish to connect to your account so that you can offer data through web services. However, in the test environment, there are no customers, so you must create an account on behalf of a customer and use the web services to simulate a situation where a customer shares a property or meter with your account.
Details on the connection and share services can be found here: http://portfoliomanager.energystar.gov/webservices/home/api/connection