Steps for automating e-signature in Salesforce

In Salesforce, I have an agreement template and some simple criteria for when it should be sent for signature (when an Opportunity goes to a specific stage). I see a bunch of semi-technical documenation, but nothing that actually says what you have to do to make it work. Can someone please define the steps needed in the Process Builder to automatically send a template for signature? (Recipient is a lookup on the Opportunity to a specific Contact.)

From what I can glean you need to use Apex to create an agreement, then can update it to send the agreement. So, I created an action for "Load Agreement Template" (passing in "Master Record ID" & "Agreement Template ID"), then a second "update records" action for the related record "[Opportunity].echosign_dev1__xxx" (passing in "Recipient (Contact)" & "Background Action"="Send"). I've given it a try, but nothing happens - no errors, no new agreement records created, etc. What am I doing wrong?