a subscription list is just a form that a user can fill in their email address that gets stored to a database table using an insert record behavior.
on the page that sends thew email, create a recordset to return the email address from the table, in universal email click the to button to set up advanced to options. in the advanced to settings, you can select to use a recordset loop for the to address.
you can also set Email Limit settings to toggle the wait time between sending emails, or set a maximum number of mails to send in a certain time period.