In early October (~5th), MAX attendees were sent an email with the subject line "You just got 120 free images from Adobe Stock" from "Adobe Creative Cloud" <email@example.com>.
It's possible it went into your bulk or junk mail box, so look/search there as well.
But even if the email was lost, you may have still received those credits in your account - check the upper right-hand corner of https://stock.adobe.com to see.
I also attended the AdobeMAX2015 conference.
I see the 120 free images... However I'm looking for the 1 free year Subscription that was offered? How do I activate the 1 free year subscription?
It's the same. With the standard Stock subscription, customers receive 10 images per month for a year... MAX attendees just received 120 images upfront, which are good for a year.