There are two possible checkout options in Ecwid:
- usual checkout with creating an account
- guest or quick checkout without creating an account (it's also called "anonymous")
So, if you get a new order, but cannot find a customer in the customers list, it means that he/she used the"guest checkout" option and didn't create a new account during purchase. So Ecwid shows their order, but doesn't show them on the Customers page. Once customer creates an account in your store, he/she will appear on the "Customers" page.
If you want to require creating an account in your store before placing an order, your can enable the “Require customers to create an account on checkout” option in your store settings: Settings → General → Cart → Require customers to create an account on checkout.
When this option is enabled, together with entering the e-mail, which is always mandatory, your customers need to create a password. After a customer creates an account, the information about their orders is stored on their account page. They also have an address book, where they can have a list of addresses where their orders can be shipped.
If you want to get information about unregistered customers, just export all of your orders to a CSV file (how to do that) — it will contain customers' info.