A Send Emails option is available within the menu displayed on clicking the Actions button in the Offer Designer toolbar:

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