Artstation - Introduction to Gaea
https://www.artstation.com/learning/courses/QJg/introduction-to-gaea

In this course, Kem Yaralioglu will cover the fundamental nodes used for terrain creation in Gaea. This is a brief overview of all of the common nodes that he uses frequently to create landscapes. This will not necessarily cover how to create a production level landscape but will cover how to use the nodes together. This course is designed to provide a solid base for navigating, understanding, and using Gaea.