To install the nodes properly you will need to download a gma extractor, wich you will then use to extract the nodes from the compressed file of the addon with the nodes.

The gma extractor can be downloaded here:

Due to steam's dumb link removal i could only post an image of the link.

After downloading and extracting the gma extractor to your desktop, go to your steam folder, wich can usually be located in:

C:\Program Files (x86)\Steam

After locating the steam folder go to:

steamapps => common => Garrysmod => garrysmod => addons

In here you will have to locate the file of the addon containing the nodes.
After locating the file put it in the folder you put your gma extractor in, i personally put it in my desktop for easy access.

Once both the addon and the gma extractor are in the same folder, execute the gma extractor.
Once the gma extractor is running click on "convert a single file", and then select the addon you wanted to extract, after doing so hit select.

After extracting the addon you will need to open the folder that has been extracted, inside the folder you will find a file with the name of the addon, open this file and inside you will find another file named "maps", copy this file and proceed to your gmod folder.

Once you have your GarrysMod folder open, go to the folder named garrysmod and then paste the "maps" folder there, your computer will probably ask you to overwrite some files, say yes to all of them as these are the map's old nodes (wich probably dont work).

After doing all of the previous steps select the map that you downloaded the nodes for and play it, nodes should now have been applied to said map.