Connecting Express forms achieves two core goals:
To learn about creating express forms, please read: https://documentation.concretecms.org/9-x/user-guide/express/express-basics. This tutorial presumes you are already familiar with managing express forms.
The connection between your contacts and the express form is achieved by being intentional with your express attribute handles and setting them to one of the well known handles. This is how the magic happens.
If your form has an attribute with any of the following handles, a contact will automatically be created under the given contact, and form completion logged as an activity against the contact. It is recommended that you use an attribute type of "Email" for email fields.
When an express form is saved, any fields with the following handles will updates the associated express entity. At this point, login is not required in order to update.
Here's a short video walking you through the creation of an express entity, and, viewing the results in your CRM!