Save a step as a template, insert one into a new step, or start a whole sequence from a template.
Open a sequence from "Sequences".
Click "Add step".
Choose "Email".
Write the email once.
Click "Save as Template" to keep it under "Your Templates".
In any later step, click "Insert Template".
Pick a saved template; it fills the subject and body, which you can still edit.
For a whole sequence, click "Use template" at the bottom of the editor.
Pick a starter: Cold Basic, Dial Only, Webinar Invite, New Website Lead or Meeting Request. Every step is added and editable.