Sheen slider adds some extra brightness on the edges of the model. There’s a Sheen tint slider too.
Clearcoat adds an extra layer of glossiness, with its own roughness value, useful when simulating car paint, eyes and others materials with a transparent and reflective layer.
Transmission slider mixes between opaque and glass-like transmission behaviour. A Transmission Roughness can be set.
IOR is the real physiks Index Of Refraction value of the glass-like simulation.
In Eevee and LookDev shading mode turn on Raytracer.