Create user from customer

We do not see how to create a user from a customer, is this possible? Also not for contacts, we supposed that a user could be somehow linked to a customer directly or via contact.

Customers are linked via Contacts. When a user signs up, the Contact’s orders are shown.

And how are they linked? by the email? We do not see something like “create from contact” or a contact field when creating a new user from the administration.

Yeah - linked by contact_email