Good evening Susan and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
I would love to help you with this topic.
The first thing I would recommend is making sure you go through the following guide precisely: http://theeventscalendar.com/knowledgebase/new-user-primer-the-events-calendar-and-events-calendar-pro/
As you can see, you first need to download, install and activate the Events Calendar Pro before being able to enter the license.
From the looks of it, that is not currently the case.
Let me know how that goes.
Best regards,
Geoff B.