The TGCs in the "Human PT SSS shaders" folder contain path tracing shader setups for different body parts. Feed the image map shaders with the appropriate texture maps that come with your model.
Of course it only works with the path tracer. 
It is recommended to increase the max ray depth, if you want to use several (SSS) glass shaders.

The "Eyeball" folder contains an eyeball model in OBJ format (the eyeball itself and the cornea), TGCs that contain PT shaders for both, and the needed texture maps.
Of course you can load the model in TG if you like, but it's mainly meant for replacing the eyeball objects of any human character model, since a lot of them have really crappy eyes, and the eyes are very crucial to make a CG character look realistic.
So, here is a short description of what I do most of the time, when I'm editing a character model in another 3D app, before I import it into TG:
First I rescale it. I use one of the Xoio characters as scale reference, that already have the right size.

https://xoio-air.de/2014/3d-people-model-set/#more-2805

Make sure your object has the pivot between the feet, and it should be at 1,1,1.
Then I replace the existing eyeballs with my eyeball obj file. Set the pivot of the new eyes to 1,1,1 as well, and export the object completely. Import it into TG, and use the appropriate TGCs with the shader setups for the eyes.
You may have to reload the texture maps, since the location of the textures, that's stored in the TGCs shows where they are on MY computer...
You can resave the TGCs with your own location for later use.
Once again, don't forget to increase the max ray depth here as well.

Have fun, and show us what you do with it!