If you're new to YDK and model-driven APIs, this blog post will help you understand the basics
Simplifying Network Programmability with Model-Driven APIs
If you're looking for an intro where you can just sit back and watch, see this NANOG introduction on YouTube:
NANOG 68 Ok We Got YANG Data Models Now What - YouTube
Both of these two resources should give you not just an overview of the technical aspects, but tell you why you should care.
Happy reading/watching!
