The Send Emails button is displayed in the Audience Designer toolbar:

If clicked when the current Audience Designer contains unsaved changes, or when the audience therein is invalid, a warning message is displayed.
Clicking the button at a valid, saved audience displays the Send Emails training aid, in which the following interfaces are shown in sequence:
•Ready to send some emails?
•Choose an existing Email
•Configure your Interaction
•Running your Interaction
•Interaction Created