How should I import synty assets according to following hints

Help
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1

Godot Version

4.5

Question

Importing Synty assets(POLYGON_NatureBiomes_AridDesert_SourceFiles_v2) following the tutorials(1 and 2), so far so good, able to find out the textures of each fbx according to the hints of MaterialList_PNB_Arid_Desert.txt, but there are some hints I can’t figure out, like this one

Prefab Name: SM_Env_Rock_Small_06
    Mesh Name: SM_Env_Rock_Small_06
        Slot: Rock_Triplanar_01 (Uses custom shader)

How should I import this “SM_Env_Rock_Small_06.fbx”? Like which texture I should use(this one do not specify the name of the texture)?
the meaning of “use custom shader”?

There are some textures name with “rock”, like “Rock_Lava_Emission_01.png”, “Rock_Lava_Texture.png”, “Rock_Lava_Normals.png”(these 3 belong to the same group I guess), “Rock_Texture_01.png”(this one do not have emission, normals) etc.

Thanks