The Marmoset tutorial is quite ok.
http://www.marmoset.co/toolbag/learn/pbr-practice
translation chart MTB->UE4:
albedo -> diffuse
microsurface -> roughness (inverted)
reflectivity -> specular
fresnel -> NO INPUT (automatically derived by BRDF model and specular-metal)
ambient occlusion -> ambient occlusion
cavity -> NO INPUT (you need to mult your maps either in diffuse and/or spec depending on the use)