The one you're showing uses metal/rough.
Main difference with specular is that in the metal workflow metals' specular colors are in your basecolor/albedo. Non-metals either all use the same value or have a seperate input.
The metallic map is a mask to show which areas are made of metal and which not. Metal with some dust or thin oxidization can sometimes have a grey color, but your metallic will be mostly black and white. White is metal, black non-metal.
Roughness is the exact opposite of glossiness. If you know how to make a gloss map, just invert it. So black is smotth, white is rough.
Marmoset has some pretty good explanations:
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https://www.marmoset.co/posts/physically-based-rendering-and-you-can-too/-
https://www.marmoset.co/posts/pbr-texture-conversion/