Even if you don’t know nothing about SDN (not even what is it), i recommend you to spend some time reading videos from Tim McConnaughy.
This SD-WAN ones is amazing, mainly the introductory history - that I bet will make you wanna watch the videos, mixing analogies and useful learning.
It is the history of Cletus, the fortunate (or unfortunate?) inheritor of some very high-tech stuff who needs an SD-WAN deployment to simplify it all. Follow Cletus and his expanding business use cases - and learn a lot of concepts meet those new business requirements.
And here you already have a spoiler from Wikipedia (on What is SDN-WAN):
SD-WAN is an acronym for software-defined networking (SDN) in a wide area network (WAN). SD-WAN simplifies the management and operation of a WAN by decoupling the networking hardware from its control mechanism. This concept is similar to how software-defined networking implements virtualization technology to improve data center management and operation.
A key application of SD-WAN is to allow companies to build higher-performance WANs using lower-cost and commercially available Internet access, enabling businesses to partially or wholly replace more expensive private WAN connection technologies such as MPLS.