Correct, first link. The I/o didn’t work when I tried it.
Did you use the correct method for linking your nodes?
You need to read all three and may also need to create a material and use the jme PBRLighting material definition and manually link your assets there.
You will also need to add a light probe to your game.
and read,
https://wiki.jmonkeyengine.org/jme3/advanced/pbr_part1.html
If you want to convert images to a texture you will need a third party app to make your materials, like Materialize - handy free tool that converts an image to PBR textures
or
https://www.allegorithmic.com/products/bitmap2material
The good thing is that as of 2.8 gltf is already included.
Edit: substance vs materialize. I found materialize produced the best results by far and its free.
Edit: PBR kicks ass once you get the pipeline down.