Its really quite simple. You can have shiny or rough wood, stone etc, that’s controlled by the roughness map. If you have 1 (or white), its 100% rough and won’t reflect anything, it is 0 (or black) it will reflect a lot.
Meatless the colour of the reflection and the albedo. If metallic is 1 (or white) then the Albedo will be black, and the reflections will be colourised by the albedo (for instance a yellow metal like gold with yellow highlights. If the metallic is 0 (or black) then the Albedo will be the colour in the texture you supply.
Thing you are missing in your scene is a reflection probe or a sky so supply the reflections that work with PBR. and that is why your metal is black, basically metals are black albedo with a lot of reflection, you need the reflection environment to fill in the missing information.