Hi Spark :-) PBR is rewarding but will take you a little time experiment with to get comfortable with it.
Note: As Marianna mentioned below, your grid will need to have already been updated to version 0.9.3 or to the comparable Dreamgrid version before PBR will be available for you to use there.
Here are some links to get you started that were helpful to me.
My work with PBR started like many with trying to make a mirror. That taught me the basics of what to look for when editing materials in the the viewer. This is the video that got me started:
https://www.youtube.com/watch?v=DvTukP_A91o&list=PLIyBt3CA...
This link will cover the basics about PBR in Second Life, and by extension Opensim. Use it as a reference as you go along:
https://www.youtube.com/watch?v=DvTukP_A91o&list=PLIyBt3CA...
Here is a great place to get free materials and assets you can upload into Opensim:
https://www.blenderkit.com/
And finally you will need a program to pack the pbr textures into a file that Opensim will be able to upload. I use this free program that's very easy to use just on your pc:
https://aiaicapta.in/gltf-packer/
And of course you can always message me here for more info. I'm usually here in the evenings or during the day during my work week.