Set a default email address that can be referenced as is or updated with a different email variable for use in, e.g., a Send Email action. You also have the option to create a collection of email addresses by activating the Set multiple values toggle.
It is worth noting that when you input an email address, its validity is automatically verified.
If you are aware of how a specific email address is constructed, you can even use an Email Address value node to dynamically build the email address using referenced inputs, such as first and last name.