By adding this type of Step to an Automation, the selected email will be sent to the contact upon reaching this point in an Automation.
Before you can add this Step to your Automation, you need to have created the email in advance and chosen the option Save for Automation. The email's status must be Unattached; in other words, it is not being used by another Automation. If you wish to use an email in multiple Automations, you should make a copy of it from its Actions menu.