Hi Kelly,
As a sales person, I am using Salesforce to send Marketo emails to my leads. Believe, it depends on how the synch is established between Marketo and Salesforce.
If you click on an individual lead in Salesforce, and scroll down you can see the Marketing Sales Insight, from where you can take action to send the marketo email.
Hope this info is useful to you.
Thanks!
Vaishali