Here's a free Principled BSDF Shader guide to help Blender users, an extract from the free PDF guide and YouTube tutorial below, hope you find it useful :D : r/learnblender
Principled BSDF — Blender Manual
How to use PBR Textures in Blender | cgbookcase.com
How to Use Blender's new ULTIMATE Shader: Principled — Blender Guru