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
texturing - Glossy BSDF on Image Texture with transparency - Blender Stack Exchange
How to Add Principled BSDF in Blender - cgian.com
Refraction BSDF — Blender Manual
Principled BSDF – Blender Knowledgebase
How to use PBR Textures in Blender | cgbookcase.com