Getting started with Shader Graph
Shader Graph is only compatible with the Scriptable Render Pipelines (SRPs), namely the High Definition Render Pipeline (HDRP) and the Lightweight Render Pipeline (LWRP). These two SRPs are available in Unity 2018.1 and later. The legacy built-in render pipeline does not support Shader Graph.
Shader Graph now comes included with the HDRP and LWRP packages. When you add either SRP to your project, Unity automatically loads Shader Graph.