Hello, sspropane.
I'll guide you in adding a customer without an email address in QuickBooks.
You don't actually need to enter a customer's email address when adding them. You can leave the Email box as blank and the system will let you add them normally.
The only field you would need to fill in is the Display name as box. Though, you can also enter the information on the name boxes.

If you need more help adding your customers, you can check this article: Add and manage customers in QuickBooks Online.
After adding your customers, do you need help recording sales receipts, invoices and other transactions? Check out the guides in our Sales and customers topic page.
I'm ready to help you sort out your other lists in QuickBooks Online. I'll keep this thread open for your reply. I can also assist you with any other concerns.