Sites and accounts
In RAI, a "Site" means a website. An "Account" is a customer account where you store all the details about the customer who owns the site(s), for example their name, email, business information, etc.
Accounts are placeholders for sites. All sites must belong to an account - accounts and sites are always bound together. There may be several sites attached to one account.
One account, multiple websites
In most use cases, a customer will have one account with one site attached to it. However, there may be cases where one account will have several sites, for example if a customer owns three restaurants and wants a unique website for each of them.
Email addresses are mandatory in RAI to have accounts. A customer may have several accounts on the same email address.
Subscriptions determine the product and permissions in the site Editor. Add-on features such as E-Commerce and CRM are subscriptions that need to be added to sites via RAI in order to function. For example, a customer will not be able to operate a web shop on the platform if an E-Commerce subscription has not been purchased.
Subscriptions are usually attached to sites, but not always. Domains and emails, for example, do not belong to a specific site when purchased and need to be attached manually.
Read more about how to add and manage subscriptions here.