Substance Designer

About using Substances:

The Substance Plug-in adds the Substance map in the Material / Map Browser so you can read SBSAR files created in the Substance Designer.

It is better to use the Slate Material Editor to compose with Substance materials, so it is easier to attach a single Substance to the various material channels instead of applying a Substance to each channel as is normally the case when configuring the Compact.

As soon as you put the Substance map in Slate and access its parameters, you will see the Load Substance button to load the SBSAR file you want, as shown in the first image attached.
After the Substance is loaded appear its parameters just below and hence it depends on who created the SBSAR.

When you connect Substance to VRayMtl's Diffuse Slot, for example, it will automatically create the Substance Output, which is the map that defines which texture within the Substance you will use on that channel.

Each Substance can have different textures inside it, it depends on who created it, so you should choose the correct texture in each channel, in case Diffuse will use Base Color.
Note that this Substance I'm using in the example has only 3 textures, Base Color, Normal, and Roughness.
Therefore, it works in the Roughness Metalic pattern and not in Specular Glossiness.

Then, for Normal Map, just copy the Substance Output and change to Normal in the list.

While Roughness will add you to the RGlossiness Slot of VRayMtl, however, you have to change the setting to Use Roughness in the BRDF menu.