I'm the creator of the fake stone pack v2 - if you load the one tgd tat comes with the pack you can see a full project and how the fake stones are integrated into your node network. If I remember correctly the actualy fake stone group is plugged into a surface layer's child port in the shader group.
Now, when you build your own projects from scratch and want to integate the fake stones at one point, you just choose file--> insert clip file, and navigate to the fake stone tgc, open that.
Then, you connect the output of the last shader of the clip file with the child port of your last surface shader in the shader group of your project - just like in the example tgd that comes with the pack.
I may add that Terragen 2 has no plugin system like the old Terragen Classic had. You don't really install any of the NWDA preset. Instead you just save them anywhere you like, and either insert them as clip files into your new projects, or just copy and paste nodes from the tgd's that ship with them.
Regards,
Frank