Marketo will list every "Activity Type", or step it takes when sending out emails. So, "Send Email" merely tells Marketo to send out the email. As you check your results later in the day, you'll likely see "Email Delivered", and hopefully "Email Opened".
Well, I set up an A/B testing environment and I think something went wrong. I have a number of emails that say, "send email", and this has been 3 weeks now. So how do I get the emails to send, even if I have to do it manually?