This page can be found through [Design > Modular Mailer (Bulk Email) > Email Series > + ].

Series Name
The Series Name will only be displayed to store admins. Once the series has been saved with a name, Steps can be added to it. (See below.)

Series Step
A series may have one or more Steps. Each Step is an email template that will be delivered at a specified interval.

To add a Step to an Email Series, select a template to be used with the series, then designate the Delivery Date.  The Delivery Date is calculated from the time that the email recipient was added to the queue.  Clicking Save Changes to this Series will add the Step to the Series and add another slot to the Email Series Editor for a new Step to be added to it. Using this method, an unlimited number of Steps may be added to an email series.