Make relationship that take Contact Email information for Order Email (new created field)

Hi

I would like orders to have a field (Email) that will be used for Quick Find. That way when searching for an email, besides the contact, opportunities, lead associated with that email, the orders will also appear.

I know how to create the field, but what I don't know is how to make a relationship between them, so that the order will take the email from the customer.

I would appreciate some help.

Thanks!